Thank very much, but it didn’t work.
the button definitely working outside MM (tested it with Python code).
Also, is it possible to start the MMM-imageslideshow as hidden?
Here is my config:
/* Magic Mirror Config Sample
 *
 * By Michael Teeuw http://michaelteeuw.nl
 * MIT Licensed.
 *
 * For more information how you can configurate this file
 * See https://github.com/MichMich/MagicMirror#configuration
 *
 */
var config = {
	address: "0.0.0.0", // Address to listen on, can be:
	                      // - "localhost", "127.0.0.1", "::1" to listen on loopback interface
	                      // - another specific IPv4/6 to listen on a specific interface
	                      // - "", "0.0.0.0", "::" to listen on any interface
	                      // Default, when address config is left out, is "localhost"
	port: 8080,
	ipWhitelist: [], // Set [] to allow all IP addresses
	                                                       // or add a specific IPv4 of 192.168.1.5 :
	                                                       // ["127.0.0.1", "::ffff:127.0.0.1", "::1", "::ffff:192.168.1.5"],
	                                                       // or IPv4 range of 192.168.3.0 --> 192.168.3.15 use CIDR format :
	                                                       // ["127.0.0.1", "::ffff:127.0.0.1", "::1", "::ffff:192.168.3.0/28"],
	language: "en",
	timeFormat: 12,
	units: "metric",
	modules: [
		{
			module: 'MMM-ImageSlideshow',
			position: 'bottom_left',
			config: {
				imagePaths: ['modules/MMM-ImageSlideshow/Images']
		}
		},
		{
			module: "alert",
		},
		{
			module: "updatenotification",
			position: "top_bar"
		},
		{
			module: 'helloworld',
			position: 'top_bar',	// This can be any of the regions.
			classes: 'small bright',
			config: {
			text: 'The Modelevich family Magic Mirror, built by a very talented person!'
		}
		},
		{
			module: "clock",
			position: "top_bar"
		},
		{
			module: 'calendar',
            position: 'top_left',
			config: {
			urgency: 0,
			getRelative: 6,
			fade: 'false',
            timeFormat: 'absolute',
			cssStyle: 'block', // block, clean, custom, (slate is for no mirror),
				calendars: [
					{
						symbol: 'calendar-check-o ',
						url: 'http://www.vic.gov.au/themes/v6/images/VictoriaCalendar-PublicHolidays.ics'
					},
					{	// YOU GET THE FOLLOWING URL FROM YOUR GOOGLE CALENDAR PAGE
						url: 'https://calendar.google.com/calendar/ical/public/basic.ics'
					},
				],
			}
		},
		{
    		module: 'MMM-WunderGround', // Just for forecast w/css entry
    		position: 'top_right',
    		config: {
        	apikey: '', // private; don't share!
        	pws: 'pws:I', // Bentleigh East Weather Station - Very Cool
			currentweather: 1,
        	coloricon: true,
        	hourly: '1',
        	fctext: '1',
        	fcdaycount: "7",
        	fcdaystart: "0",
        	hourlyinterval: "2",
        	hourlycount: "1",
			animationSpeed: 5000,
        	alerttime: 10000,
        	alerttruncatestring: "english:",
    		roundTmpDecs: 0,
    		UseCardinals: 1,
			fade: false,
    		layout: "vertical",
			windunits: "mph",
    		sysstat: "0"
		}
		},
		{
	        module: 'MMM-Traffic',
            position: 'top_left',
            classes: 'dimmed medium', //optional, default is 'bright medium', only applies to commute info not route_name
            config: {
                api_key: '',
                mode: 'driving',
				origin: '9 Tambet Street, Bentleigh east, Australia 3165',
				destination: '96 Herbert Street, Northcote, Australia 3070',
				arrival_time: '0900', //optional, but needs to be in 24 hour time if used.
				route_name: 'Home to Work',
                changeColor: true,
                showGreen: false,
                limitYellow: 5, //Greater than 5% of journey time due to traffic
                limitRed: 20, //Greater than 20% of journey time due to traffic
                traffic_model: 'best_guess',
                interval: 60000, //2 minutes
                showWeekend: true,
                allTime: true,
                width: '300px',
                height: '300px'
            }
        },
		{
            module: 'MMM-GoogleMapsTraffic',
            position: 'top_left',
            config: {
                key: '',
                lat: -37.7685637,
                lng: 144.9943173,
                height: '400px',
                width: '550px',
				zoom: 13,
				disableDefaultUI: false
            }
        },
		{
    		module: 'voicecontrol',
    		position: 'top_right',
    		config: {
        		models: [
            	{
                	keyword: "Show Camera",
                	description: "Say 'Show Camera' to display camera",
                	file: "showCamera.pmdl",
                	message: "SHOW_CAMERA"
            	},
            	{
                	keyword: "Hide Camera",
                	description: "Say 'Hide Camera' to hide camera",
                	file: "hideCamera.pmdl",
                	message: "HIDE_CAMERA"
            	},
            	{
                	keyword: "Selfie",
                	description: "Say 'Selfie' when camera is visible",
                	file: "selfie.pmdl",
                	message: "SELFIE"
            	},
        ],
		}
		},
		{
			module: 'camera',
    		position: 'fullscreen_above',
    		config: {
			selfieInterval: 3,  // Time interval in seconds before the photo will be taken.
        	emailConfig: {
            service: 'gamil', // Email provider to use to send email with a photo.
            auth: {
        }
        }
		}
		},
		{
			module: "compliments",
			position: "lower_third"
		},
		{
			module: 'newsfeed',
			position: 'bottom_bar',
			config: {
				feeds: [
					{
						title: "The Age",
                                                url: "http://feeds.theage.com.au/rssheadlines/top.xml",
                                      },
                                        {
                                                title: "Sport",
                                                url:  "http://www.theage.com.au/rssheadlines/sport/article/rss.xml"
                                        }
                                ],
				showSourceTitle: true,
				showPublishDate: true
			}
		},
{
		    module: 'MMM-Buttons',
		    config: {
			maxShortPressTime: 1000,
		        buttons: [
		            {
		                pin: 18,
		                name: "MMM-ImageSlideshow",
		                shortPress: {
		                    notification: "REMOTE_ACTION",
		                    payload: {
                            action: "HIDE",
                            module: "module_0_MMM-ImageSlideshow"
                        }
		                },
                          longPress: {
                          notification: "REMOTE_ACTION",
                          payload: {
                          action: "SHOW",
                          module: "module_0_MMM-ImageSlideshow"
                                          }
                                 },
		       },
		     ]
		   }
		},
		{
		module: 'MMM-Remote-Control', 
		position: 'bottom_right'
		},
	]
};
/*************** DO NOT EDIT THE LINE BELOW ***************/
if (typeof module !== "undefined") {module.exports = config;}