Implement Desktop Screen for Wayland

I like the strategy that rjkroege suggested, on making the loaf of desktop_aura
on the Ozone implementation's side:

https://codereview.chromium.org/19118003/

Signed-off-by: Tiago Vignatti <tiago.vignatti@intel.com>
patches: Track "Implement Desktop Screen for Wayland" changes