[GTK] Provide a default size for stock icons
[GTK] Properly render stock and custom icons in ImageView
[GTK] Fixed several gtk warnings

Which are caused by trying to set the Events
property when the widget is already realized.
[GTK] Implement Window.Shown/Hidden events

Also fix bounds calculation issue
[Mac] Track api changes
The backend of ImageView now gets a full Image object

Required because an image can now be a custom
drawn image.
Add unit test projects and fix some tests