gradle: update to 2.1 and android targetSdk 21

- add android-appcompat subproject
wip: Viewport sync
Animator: wip animation event
ViewController: clamp tilt in setPosition
android: refactor MapView

- merge AndroidMap + GLView into Mapview
- let MapView directly extends GLSurfaceView
remove MapActivity

- see vtm-android-start for an example use of MapView
- add MapPreferences

- update android-start
- android-example: use appcompat actionbar