Handle the room display name and its avatar at the room summary level.

- Update the room display name and its avatar url when the Room Summary is updated on state events change (see `[session: updateRoomSummary: withStateEvents:]`).
- Store the riot display room name and its avatar url in the Room Summary.
- Add a new category `MXRoomSummary+Riot` to handle avatar display.

TODO: Increase file store version in `MXFileStore.h`.

Riot/Views/RoomList/RoomCollectionViewCell.m

@@ -20,7 +20,7 @@
 
 #import "RiotDesignValues.h"
 
-#import "MXRoom+Riot.h"
+#import "MXRoomSummary+Riot.h"
 
 #import "MXTools.h"
 
@@ -171,7 +171,7 @@
         
         self.encryptedRoomIcon.hidden = !roomCellData.roomSummary.isEncrypted;
         
-        [roomCellData.roomSummary.room setRoomAvatarImageIn:self.roomAvatar];
+        [roomCellData.roomSummary setRoomAvatarImageIn:self.roomAvatar];
     }
 }