WIP: Adapt all scene change and implement Subsurface

hello

I have implented all changes in scene and plugin/scene . it include the generation of quad by subsurface.

The only one commit i not migrated is the multiple cursor commit.

I have tested : weston-subsurface, weston-scaler and supertux2

Can you review ?

For testing, it need wrapland!68 (closed) until it accepted in mainline