tracker-extract-gstreamer: Move media art parameters to MetadataExtractor
tracker-extract-gstreamer: Move media art parameters to MetadataExtractor

This allows slightly more efficient processing because the apply_*
functions can access media_art_type

hoheinzollern/tracker,outofbits/tracker,outofbits/tracker,outofbits/tracker,hoheinzollern/tracker,outofbits/tracker,hoheinzollern/tracker,outofbits/tracker,hoheinzollern/tracker,hoheinzollern/tracker,hoheinzollern/tracker,hoheinzollern/tracker,outofbits/tracker,outofbits/tracker