An update on Downtime.

The update is that Downtime is obsolete.  Replaced by the
ability to define multiple named schedule calendars.

 - Make changes to ZenModeConfig to properly model manual
   and automatic rules.
 - Refactor the zen mode helper (and supporting classes) to
   properly handle / report multiple claims on zen mode.
   The "manual" rule (specified by the user in the UI) vs
   one or more automatic rules.
 - Automatic rules are still backed by condition providers,
   but the layering is now cleaner.  ConditionProviders is now
   completely generic, has no ties to zen mode.
 - Specifically, the new layering for zen mode (below noman) is:
   ZenModeHelper: Source of truth for zen state
     ZenModeFiltering: Subhelper dedicated to filtering rules.
     ZenModeConditions: Subhelper dedicated to managing automatic rules.
       ConditionProviders:  Underlying engine for reporting named boolean state.
 - Migration story for users with existing downtime config, migrated
   to a single new calendar named downtime.
 - For users with no existing downtime, two default calendars are created
   for weeknights + weekends (icu4j for all locales will be done in a followup).
 - Remove obsolete DowntimeConditionProvider/NextAlarmConditionProvider and tracking.
 - Clean up obsolete resources.
 - Add common zen summary description string computation.
 - Add proper noman wrappers for the new model.
 - Change the semantics of the global zen setting.  It is now read-only.  Setters
   must call noman, added a "reason" to all calls for better attribution.
 - Update zenmodepanel + volumedialog to the new model.
 - Display the one or more automatic rules in the new zen footer summary.
 - "Snooze" the automatic rules when the user explicitly turns zen off.

Bug: 20064962
Change-Id: Idd9deb865a6035ad0cfae660198dccb517e6d7cc