Add new loading indicators

Riot/Modules/MatrixKit/Controllers/MXKViewControllerActivityHandling.h

@@ -35,6 +35,14 @@
  */
 @property (nonatomic) UIActivityIndicatorView *activityIndicator;
 
+/**
+ A view controller may choose to implement a completely custom activity indicator (e.g. shared toast notification),
+ 
+ In this case the default `activityIndicator` will be hidden, and the view controller is responsible for overriding
+ `startActivityIndicator` and `stopActivityIndicator` methods to show / hide the custom activity indicator.
+ */
+@property (nonatomic, readonly) BOOL providesCustomActivityIndicator;
+
 /**
  Bring the activity indicator to the front and start it.
  */