Introduce a Lifecycle for system services

Provide an abstract class for system services to extend from,
similar to the android.app.Service.

This will allow services to receive events in a uniform way,
and will allow services to be created and started in the
correct order regardless of whether or not a particular
service exists.

Similar to android.app.Service, services are meant to implement
Binder interfaces as inner classes. This prevents services from
having incestuous access to each other and makes them use the
public API.

Change-Id: Iaacfee8d5f080a28d7cc606761f4624673ed390f