Notification settings updates

- Text changes
- Show channels on the app settings screen (again)
- Hide most of the channel settings under 'advanced' (note: this hides
  the footer preference(s) also, at the moment. the functionality
  to exclude those is coming in a later cl)
  - Add a 'show notifications' toggle for each app created group

Bug: 63927402
Test: make RunSettingsRoboTests

Change-Id: I9906ef943d05e1915061b59294a25d81c4e6cbb5