feat(JitsiLocalTrack): make mute/unmute more resilient

Instead of failing with an error if another operation is in progress, which is
impossible to know as a user, chain them using the primises API.

JitsiTrackError.js

     = 'Track has been already disposed';
 TRACK_ERROR_TO_MESSAGE_MAP[JitsiTrackErrors.TRACK_NO_STREAM_FOUND]
     = 'Track does not have an associated Media Stream';
-TRACK_ERROR_TO_MESSAGE_MAP[JitsiTrackErrors.TRACK_MUTE_UNMUTE_IN_PROGRESS]
-    = 'Track mute/unmute process is currently in progress';
 TRACK_ERROR_TO_MESSAGE_MAP[JitsiTrackErrors.NO_DATA_FROM_SOURCE]
     = 'The track has stopped receiving data from it\'s source';
 

JitsiTrackErrors.js

  */
 export const TRACK_IS_DISPOSED = 'track.track_is_disposed';
 
-/**
- * An error which indicates that track is currently in progress of muting or
- * unmuting itself.
- */
-export const TRACK_MUTE_UNMUTE_IN_PROGRESS = 'track.mute_unmute_inprogress';
-
 /**
  * An error which indicates that track has no MediaStream associated.
  */

doc/API.md

         - CONSTRAINT_FAILED - getUserMedia-related error, indicates that some of requested constraints in getUserMedia call were not satisfied.
         - TRACK_IS_DISPOSED - an error which indicates that track has been already disposed and cannot be longer used.
         - TRACK_NO_STREAM_FOUND - an error which indicates that track has no MediaStream associated.
-        - TRACK_MUTE_UNMUTE_IN_PROGRESS - an error which indicates that track is currently in progress of muting or unmuting itself.
         - CHROME_EXTENSION_GENERIC_ERROR - generic error for jidesha extension for Chrome.
         - CHROME_EXTENSION_USER_CANCELED - an error which indicates that user canceled screen sharing window selection dialog in jidesha extension for Chrome.
         - CHROME_EXTENSION_INSTALLATION_ERROR - an error which indicates that the jidesha extension for Chrome is failed to install.

modules/RTC/JitsiLocalTrack.js

 const logger = getLogger(__filename);
 
 /**
- * Creates Promise for mute/unmute operation.
+ * Creates Promise for mute/unmute operation. Mute operations are chained, so
+ * this function can be called as many times as needed in a row and operations
+ * will be executed in a serialized fashion.
  *
  * @param {JitsiLocalTrack} track - The track that will be muted/unmuted.
  * @param {boolean} mute - Whether to mute or unmute the track.
  * @returns {Promise}
  */
 function createMuteUnmutePromise(track, mute) {
-    if (track.inMuteOrUnmuteProgress) {
-        return Promise.reject(
-            new JitsiTrackError(JitsiTrackErrors.TRACK_MUTE_UNMUTE_IN_PROGRESS)
-        );
-    }
+    const doMute = () => track._setMute(mute);
 
-    track.inMuteOrUnmuteProgress = true;
+    track._mutePromise = track._mutePromise.then(doMute, doMute);
 
-    return track._setMute(mute)
-        .then(() => {
-            track.inMuteOrUnmuteProgress = false;
-        })
-        .catch(status => {
-            track.inMuteOrUnmuteProgress = false;
-            throw status;
-        });
+    return track._mutePromise;
 }
 
 /**
 
         this.deviceId = deviceId;
         this.storedMSID = this.getMSID();
-        this.inMuteOrUnmuteProgress = false;
+
+        /**
+         * The promise which indicates a mute or unmute operation is in
+         * progress.
+         *
+         * @private
+         * @type {Promise}
+         */
+        this._mutePromise = Promise.resolve();
 
         /**
          * The facing mode of the camera from which this JitsiLocalTrack