Chat screen implementation

Handle event selection when user taps on text message view.

Note: The read receipts are still displayed by MatrixKit, they may overlap timestamp until Vector handle them correctly.

Vector/Model/Room/RoomDataSource.h

@@ -21,4 +21,9 @@
  */
 @interface RoomDataSource : MXKRoomDataSource
 
+/**
+ The event id of the current selected event if any. Default is nil.
+ */
+@property(nonatomic) NSString *selectedEventId;
+
 @end