DeskClock: Properly align settings

* The alarm volume setting doesn't look as it should
* Copied "preference_volume_slider" from Settings (used in Settings->
  Sound) and stripped by stuff we don't need (suppression_text,
  widget_frame)
* Looks like without providing an initial icon, the layout would not
  inflate the space for it properly, so provide the default one

Test: manual - Tested the DeskClock UI manually and checked that
alarm volume preference is aligned to the rest of the preferences

Change-Id: Ib1e36c36c8fb5c91992dc8163fe84564b647bdbd