Spin off smartspace behavior into SmartspaceController

Spins off the logic for manging the smartspace view into
LockscreenSmartspaceController. In addition to just cleaning things up,
this allows us to expose the current contents of the smartspace to any
listeners that might be interested (there's an interested listener in
the following CL).

Bug: 186481467
Test: atest
Change-Id: I117afdc984215128ec47dfd3190d1685757c0f69