App Extension - Fix matrix session handling

The matrix session should be handled by the ShareExtensionManager. This manager is able to prepare, suspend and resume the session.
Note: The ShareViewController is reloaded each time the extension is launched

RiotShareExtension/Model/ShareExtensionManager.h

@@ -19,6 +19,12 @@
 
 @class ShareExtensionManager;
 
+/**
+ Posted when the matrix session has been changed.
+ The notification object is the matrix session.
+ */
+extern NSString *const kShareExtensionManagerDidChangeMXSessionNotification;
+
 /**
  The protocol for the manager's delegate
  */
@@ -58,6 +64,11 @@
  */
 @property (nonatomic) NSExtensionContext *shareExtensionContext;
 
+/**
+ The associated matrix session (nil by default).
+ */
+@property (nonatomic, readonly) MXSession *mxSession;
+
 /**
  A delegate used to notify about needed UI changes when sharing
  */