Conference call: Add ongoing conference call banner

Vector/Views/RoomActivitiesView/RoomActivitiesView.h

@@ -54,6 +54,14 @@
  */
 - (void)displayTypingNotification:(NSString*)labelText;
 
+/**
+ Display an ongoing conference call.
+ Replace the current notification if any.
+
+ @param labelText the current typing message.
+ */
+- (void)displayOngoingConferenceCall:(NSString*)labelText;
+
 /**
  Remove any displayed information.
  */