Implement onDestroy handling for providers.

Implement onDestroy that host applications will call for CardProviders.
Call CMHomeApiManager.destroy() when this happens to release
ContentObservers and unregister the BroadcastReceiver.

Change-Id: I47c19a301d01ecb89cb545feb6dec6a237704853
Add Javadocs for SDK.

Change-Id: Id402b7cd5f4522bf0bb35835d492398ee9ae09cc