PVRChannelsOSD: added commands for switching channel group (left/right)

XBMC's PR #2246 (https://github.com/xbmc/xbmc/pull/2246) replace
hardcoded left/right group switching with proper action handling.

This PR adds the action handling to the PVR channel osd.
Merge pull request #590 from xhaggi/pvr

PVRChannelsOSD: added commands for switching channel group (left/right)
videoosd: fix wrong onfocus rewind and forward button texture
fix: no osd on paused live tv stream (fix PR #594)
epg: fix title/plot alignments and sizes
fix: alignment of recoding and timer icon in epg grid (fix PR #551)
Merge pull request #595 from xhaggi/pvr

fixes for the pvr section + some improvements
merge fix
Merge branch 'master' into test