feat(ConferenceTimer): Add config option to hide.

config.js

     // otherwise the app doesn't render it.
     // moderatedRoomServiceUrl: 'https://moderated.jitsi-meet.example.com',
 
+    // Hides the conference timer.
+    // hideConferenceTimer: true,
+
+    // Sets the conference subject
+    // subject: 'Conference Subject',
+
     // List of undocumented settings used in jitsi-meet
     /**
      _immediateReloadThreshold

react/features/base/config/configWhitelist.js

     'forceJVB121Ratio',
     'gatherStats',
     'googleApiApplicationClientID',
+    'hideConferenceTimer',
     'hiddenDomain',
     'hideLobbyButton',
     'hosts',

react/features/conference/components/native/NavigationBar.js

  */
 function _mapStateToProps(state) {
     return {
-        _conferenceTimerEnabled: getFeatureFlag(state, CONFERENCE_TIMER_ENABLED, true),
+        _conferenceTimerEnabled:
+            getFeatureFlag(state, CONFERENCE_TIMER_ENABLED, true) && !state['features/base/config'].hideConferenceTimer,
         _meetingName: getConferenceName(state),
         _meetingNameEnabled: getFeatureFlag(state, MEETING_NAME_ENABLED, true),
         _visible: isToolboxVisible(state)

react/features/conference/components/web/Subject.js

 type Props = {
 
     /**
-     * Whether then participant count should be shown or not.
+     * Whether the conference timer should be shown or not.
+     */
+    _hideConferenceTimer: Boolean,
+
+    /**
+     * Whether the participant count should be shown or not.
      */
     _showParticipantCount: boolean,
 
      * @returns {ReactElement}
      */
     render() {
-        const { _showParticipantCount, _subject, _visible } = this.props;
+        const { _hideConferenceTimer, _showParticipantCount, _subject, _visible } = this.props;
 
         return (
             <div className = { `subject ${_visible ? 'visible' : ''}` }>
                 <span className = 'subject-text'>{ _subject }</span>
                 { _showParticipantCount && <ParticipantsCount /> }
-                <ConferenceTimer />
+                { !_hideConferenceTimer && <ConferenceTimer /> }
             </div>
         );
     }
  * @param {Object} state - The Redux state.
  * @private
  * @returns {{
+ *     _hideConferenceTimer: boolean,
+ *     _showParticipantCount: boolean,
  *     _subject: string,
  *     _visible: boolean
  * }}
     const participantCount = getParticipantCount(state);
 
     return {
+        _hideConferenceTimer: Boolean(state['features/base/config'].hideConferenceTimer),
         _showParticipantCount: participantCount > 2,
         _subject: getConferenceName(state),
         _visible: isToolboxVisible(state) && participantCount > 1