Fill in ActivatableNotificationViewController.

This removes calls to Dependency.get() from
ActivatableNotificationView. The controller still isn't
fully fleshed out due to the current structure of the code,
but it is a step in the right direction.

Future CL's will add more controllers for futher subclasses.

Bug: 14724574
Test: atest SystemUITests
Change-Id: If72c1e19af69c41f9c557147e13593b33ba32bce