Chat Screen: Improve Room header

- add topic in preview header
- remove new line characters in topic string
- collapse expander header when user scrolls it down.

Vector/ViewController/RoomViewController.h

@@ -25,6 +25,7 @@
 @interface RoomViewController : MXKRoomViewController <UISearchBarDelegate, UIGestureRecognizerDelegate, RoomTitleViewTapGestureDelegate>
 
 // The expanded header
+@property (weak, nonatomic) IBOutlet UIScrollView *expandedHeaderScrollView;
 @property (weak, nonatomic) IBOutlet UIView *expandedHeaderContainer;
 @property (weak, nonatomic) IBOutlet NSLayoutConstraint *expandedHeaderContainerHeightConstraint;