SleepTimerEdit: indicate if sleeptimer is active or not

And give an indication about the remaining time
In addition fix a bug when the sleeptimer config was changed

Thanks Dima73 for the suggestions
eDVBScan: add sanitycheck on m_ch_current

dc4498c8361646bff74b542a88e046f7b79fbc2d could cause a segfault
Merge branch 'master' of git://git.code.sf.net/p/openpli/enigma2