Change zen schedules page to use switches.

Also add clearer summaries for schedule and calendar events (rather than just "Off" and "On"): for schedules, list the days & times for which the schedule is active, and for events, the calendar whose events it triggers on.

Bug: 190180868
Bug: 215564123
Test: manual for switches, ZenRuleScheduleHelperTest for descriptions

Change-Id: I3ad579503adae0a66dfa3093b4e3df77db0ede31