Added zen settings messages and calls preferences.

- Made ZenModeSettings and ZenModeBehaviorSettings a DashboardFragment
- Switches in ZenModeBehaviorSettings all have their own preference controllers
- Instead of a dropdown, messages & calls have their own pages & preference controllers
- Added basic turn on/off DND button in settings (dialog not yet implemented)

Bug: 63077372
Fixes: 69057767
Test: make -j40 RunSettingsRoboTests
Change-Id: I1c70f77053713f66f873ee578477f23cfd7985bb