Hotkey: Add next/previous to timeshift/movieplayer exception keys

Thanks Satkiekerd
Add sanity check for tuners with an empty sat list.

Signed-off-by: littlesat <littlesat99@yahoo.com>
Add new PluginDescriptor WHERE_CHANNEL_CONTEXT_MENU

Signed-off-by: Littlesat <Littlesat99@yahoo.com>
Hotkey: Add hotkey function showServiceListOrMovies
ChannelSelection: Do not add context menu plugin twice
Merge branch 'master' of git://git.code.sf.net/p/openpli/enigma2