rev1:
This is a first rough split-up of Compositor class. It works but there is possible more functionality that could be put into one of the child classes only.
rev2:
The `isCreated` function is only used in a single Q_ASSERT. I'm not in favor of keeping it. We should not need an assert for stuff like that. The currentRefreshRate extern function is there for no apparent reason.
rev3:
Move Suspend reasons into X11Compositor
rev4:
Check for overlay window in X11Compositor class
rev5:
Use new slots syntax
rev6:
Release selection in X11Compositor
rev7:
Remove optimization by compositing initialized check
rev8:
Setup only in Compositor child classes
rev9:
Remove reinit dbus method, remove restart function and streamline setup
rev10:
XWayland destroyed signal only in Wayland compositor and move initial unusedSupportPropertyTimer call into X11Compositor.