fix(SS): Add toggle parameter

conference.js

     },
 
     /**
-     * Toggles between screensharing and camera video.
+     * Toggles between screen sharing and camera video if the toggle parameter
+     * is not specified and starts the procedure for obtaining new screen
+     * sharing/video track otherwise.
+     *
+     * @param {boolean} [toggle] - If true - new screen sharing track will be
+     * obtained. If false - new video track will be obtain. If not specified -
+     * toggles between screen sharing and camera video.
      * @param {Object} [options] - Screen sharing options that will be passed to
      * createLocalTracks.
      * @param {Array<string>} [options.desktopSharingSources] - Array with the
      * 'window', etc.).
      * @return {Promise.<T>}
      */
-    toggleScreenSharing(options = {}) {
+    toggleScreenSharing(toggle = !this._untoggleScreenSharing, options = {}) {
         if (this.videoSwitchInProgress) {
             return Promise.reject('Switch in progress.');
         }
             return Promise.reject('No screensharing in audio only mode');
         }
 
-        if (!this._untoggleScreenSharing) {
+        if (toggle) {
             return this._switchToScreenSharing(options);
         } else {
             return this._untoggleScreenSharing();