servicemp3: Implement iServiceInformation getEvent for EPG

Servicemp3 didnt shown EPG due to lack of getEvent, altough valid sid,onid,tsid was set.
Also epgcache only allowed idDVB to query for EPG cache. idServiceMP3 (4097) added in eServiceReference
Extra check added to allow idServiceMP3 to query EPG cache.

More information here: http://openpli.org/forums/topic/31451-epg-with-gstreamer-servicemp3/