[pvr] add optional support for playing recordings from epg timeline or epg osd

This allows user to play recording through programme info dialog, which is shown by clicking on programme in the past in epg timeline or epg osd view. It also switches to a recording playback from epg search result if selected programme has one.
Programmes with associated recordings are shown with HasRecording marker (skin.confluence).
To associate recording to a programme pvr client should set recording id for corresponding epg tag. This will turn on epg updates on recordings update.
If pvr client doesn't use epg-recordings linking, then no such updates occured and everything else remains as it is now (views, switching to live stream, etc.).
If pvr backend has ability of recording everything (e.g. network pvr), then pvr client should implement its own recordings update logic to trigger recordings update on each programme end.
More info at http://forum.xbmc.org/showthread.php?tid=179792