Internal API for cross-task Activity used by assistant.

29091742

A new internal API has been created for use by assistant
to launch an Activity Transition from a non-Activity.

The ActivityOptions are also passed along when using
a spring board Activity so that the shared elements
can be properly synchronized.

This also fixes TransitionManager.endTransition so
that it forces Transitions to end the animations.

Change-Id: Id18d9765bfc0c7b438e17966455aa66d3fa3aeda