Refactor code that checks for settings that suppress alarms

Bug: 32196863
Bug: 32198258
Bug: 32011667
Test: all testing performed manually

This code was located in the DeskClock activity, but has been moved
to SilentSettingsModel, a new delegate of DataModel. The settings
themselves are now inspected on a background thread. A new check
was added to inspect clock notification blocking.

Change-Id: I9eae5832bfed201f22ac899bb419334f799dd104