[BREAKING CHANGE] Refactor for multiple surfaces

Replace target.surface with target.surfaces, and introduce
the concept of an active surface at target.surface. By default
surfaces become active when focused.

Bonus:
* Move debug bar setup from target to surface.
* Move import rules to config.

Change-Id: I5c2afe424a3cc4e9973af4a657553f1634c9a7e1