Changes JitsiConference.getLocalTracks and JitsiParticipant.getTracks to return cloned array of tracks

JitsiConference.js

  */
 JitsiConference.prototype.getLocalTracks = function () {
     if (this.rtc) {
-        return this.rtc.localStreams;
+        return this.rtc.localStreams.slice();
     } else {
         return [];
     }

JitsiParticipant.js

  * @returns {Array.<JitsiTrack>} The list of media tracks for this participant.
  */
 JitsiParticipant.prototype.getTracks = function() {
-    return this._tracks;
+    return this._tracks.slice();
 };
 
 /**