[mythtv-cmyth] Fix live recording done

Completing live recording was not handle. It was not possible to keep next recording in the chain.
Here i reset m_liveRecording flag on event DONE_RECORDING. Also i clean code around this flag.
[mythtv-cmyth] Menuhook action 'Keep LiveTV recording': Bail if not LiveTV

Recording group is updated to "Default". So process action only on LiveTV recording.