CC-5627 : Check all Application_Common_DateHelper calculations that use
timezone.

* Fixed GetPlayOrderRange to be consistently return everything in UTC.
* ApiController liveInfoAction now returns everything consistently in
  the station timezone. This fixes negative remaining time that could
  occur in the embeddable JS Airtime widgets if you were logged in to
  Airtime while you viewed your website. (The widgets display in
  the browser's local time.)
* ScheduleController getCurrentPlaylistAction() returns everything
  consistently in the user timezone now.
Merge branch '2.5.x' of github.com:sourcefabric/Airtime into 2.5.x