Fixed https://github.com/vector-im/vector-ios/issues/246: universal link on an unjoined room + an event iD is not properly managed

Vector/Model/Room/RoomPreviewData.h

@@ -43,6 +43,12 @@
  */
 @property (nonatomic) MXSession *mxSession;
 
+/**
+ The id of the event where to start to show the room once joined.
+ It is non nil only for permalinks to rooms the user has not joined yet.
+ */
+@property (nonatomic) NSString *eventId;
+
 /**
  Preview information.
  They come from the `emailInvitationParams` or [self fetchPreviewData].