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/Search/MessagesSearchResultTextMsgBubbleCell.m

@@ -19,8 +19,6 @@
 
 #import "RiotDesignValues.h"
 
-#import "MXRoom+Riot.h"
-
 @implementation MessagesSearchResultTextMsgBubbleCell
 
 - (void)customizeTableViewCellRendering
@@ -43,7 +41,7 @@
         MXRoom* room = [bubbleData.mxSession roomWithRoomId:bubbleData.roomId];
         if (room)
         {
-            self.roomNameLabel.text = room.riotDisplayname;
+            self.roomNameLabel.text = room.summary.displayname;
         }
         else
         {