Zen: Improve zen mode panel condition selection.

 - Decouple condition requests from expansion, now
   pre-request when zen panel unhidden.
 - Animate zen mode panel expansion.
 - Improve default selection logic, ensure something
   is selected as soon as we are in the expanded state.
 - Tweak visual spacing.
 - Map null condition to Indef properly when we start
   out in zen.
 - Avoid unnecessary condition teardown when the conditions
   are updated but unchanged from current.
 - Cap number of optional conditions to display, default=3.

Bug: 18335618

Change-Id: I007b7c3b2e75e2b42805af240684aa8581e9951a