[Window Manager] Show a thumbnail along with the window icon in the notification.
[Notification applet] camelCase-refactoring victim.
[Message Tray] Check for pending notifications before acting. Plus some cleanup.
Revert "cinnamon-settings: use Gtk.Clutter.init() instead of Clutter.init()"

This reverts commit 8d7f83c91459b7eab8dfdc217cc3f40cafc74b5d.