scan: ignore onid/tsid when adding transponders

the current transponder id is irrelevant
scan: add basic T2_delivery_system_descriptor support

only with external FrequencyListDescriptor for now
Small changes regards parental control in ChannelSelection Context Menu

Thanks Dima73
Merge branch 'master' of git://git.code.sf.net/p/openpli/enigma2 into BETA