Settings: An update on Downtime.

 - Migrate settings to the new zen mode state model.
 - Remove downtime settings.
 - Add automatic rule management page (add/remove)
 - Bind new automatic schedule rules to detail editor.
 - Clean up a few found miscapitalized string captions.
 - Migrate zen switch to report the shared summary string.

Bug: 20064962
Change-Id: Ia561e7f77c90c962729240b4d51ba1915297f64a