Hotkey: Only 'hotkey' play, pauze, rewind... buttons when we are in live-TV

As suggested by greatred - as also I think this makes sense...
http://forums.openpli.org/topic/35098-hotkey-problems-suggestions/page-19
changed keyboard's keycodes KEY_BACK/KEY_FORWARD as device dependents and removed some nonsencial using KEY_BACK code

Signed-off-by: pieterg <pieterg@users.sourceforge.net>
Merge branch 'master' of git://git.code.sf.net/p/openpli/enigma2