Settings: Quiet hours: Bring back summaries

On languages with very long words e.g. German the new UI look awful.
Bring back summaries to make it look a bit better.

Change-Id: I2ac61e620a24731b65aaf3a962010d8d842c8daf
Settings: Remove redundancy in description

* All these settings are under a 'Volume buttons' header.
  Avoiding duplication of 'Volume button' makes it easier for
  translators

Change-Id: I51eb2de69c2f038f13d95a8e97bde1ecf83df913