If we don't have a dedicated device identifier we should use the default
mechanismn which involves using the WAYLAND_DISPLAY or WAYLAND_SOCKET env
variable.
We are going to switch to a proper nested approach similar to the
x11 backend. Given that we don't want to run on fullscreen anymore
but just open a nested window.
With this change all backends need to emit the screensQueried signal
at some point. So far only x11 backend did not provide the signal,
wayland had a comparable delayed init mechanism. Now all backends use
the same mechanism.
Replaces the functionality of the WaylandBackend and makes it available
to all backends by providing the functionality directly in
AbstractBackend. By default a backend is not ready and the implementation
must call setReady(true) to indicate that setup has finished
successfully. The compositor won't start till the backend indicates that
it is ready.
The aim is to be able to create a plugin for each of the backends.
The following directories are created:
* backends/drm
* backends/fbdev
* backends/wayland
* backends/x11
