default: Adjust the default background

Getting a bit tired of green...
wayland: Put the MetaWaylandBuffer implementation in a new file
wayland: Move some buffer manipulation functions to meta-wayland-buffer
wayland-surface: Clean up includes
wayland: Clean up more includes
wayland: Clean up a bit more
wayland: Move MetaWaylandRegion into a new file as well
wayland: Make the MetaWaylandRegion type opaque
wayland: Make WaylandEventSource private
wayland: Remove unused variable
wayland: Remove old comments
wayland: Clump the globals code together