Added an UngrabMouseBindings function to X11XCB_WindowManager.
Don't grab bindings when registering.
Change MOVE_WINDOW back to super + left click.
Add the screen's windows to the screen's layout.
Made RegisterBindings non-const.
Made the BindingActuators inside Stack_WindowLayout take a Stack_WindowLayout argument in their constructors.
Split SetupScreens into SetupScreens and SetupWindowLayouts.
The Big Refactor:
- The Screen interface is gone.  Its functions have primarily been put into RootWindow.
- PrimaryWindow and its implementations are now ClientWindow, etc.
- WindowManager has nothing to do with WindowLayout anymore.  That's now controlled by RootWindow.