external_api: add ability to toggle lobby

modules/API/API.js

 import { isEnabled as isDropboxEnabled } from '../../react/features/dropbox';
 import { setE2EEKey } from '../../react/features/e2ee';
 import { invite } from '../../react/features/invite';
+import { toggleLobbyMode } from '../../react/features/lobby/actions.web';
 import { RECORDING_TYPES } from '../../react/features/recording/constants';
 import { getActiveSession } from '../../react/features/recording/functions';
 import { muteAllParticipants } from '../../react/features/remote-video-menu/actions';
 
             APP.store.dispatch(muteAllParticipants(localIds));
         },
+        'toggle-lobby': isLobbyEnabled => {
+            APP.store.dispatch(toggleLobbyMode(isLobbyEnabled));
+        },
         'password': password => {
             const { conference, passwordRequired }
                 = APP.store.getState()['features/base/conference'];

modules/API/external/external_api.js

     displayName: 'display-name',
     e2eeKey: 'e2ee-key',
     email: 'email',
+    toggleLobby: 'toggle-lobby',
     hangup: 'video-hangup',
     muteEveryone: 'mute-everyone',
     password: 'password',