Zen: Stateful condition panel.

When DND is on, expanded panel shows the current time
condition, or time remaining.  The last time bucket
selected is remembered as the default option for the
next time.

Move the server-side countdown helper into a proper
condition provider, but register it in-process as a
system provider.

Move common countdown condition parsing into ZenModeConfig
to reuse from system components.

Keep the manual exit condition around in zen mode config
and add plumbing for getting / listening to the
controller.

Keep the last QS detail panel around instead of
recreating it every time.

Fix the time condition's plus and minus button
enabling logic, and enhance the click handler to
deal properly with the next or previous bucket.

Bug:15344758
Change-Id: Ie7018a1c20e20f6d7e5f9e7874188374e6f8e2ab