Implement host window rendering through libhybris

This introduces a new server instance inside LunaSysMgr to accept shared rendering buffers
from remote clients like WebAppMgr. The central compositor instance accepts the buffers
and forwards them to the corresponding host window which wraps them into the right
rendering object of the UI.

Open-WebOS-DCO-1.0-Signed-Off-By: Simon Busch <morphis@gravedo.de>