Add support for PERFORMER field for ID3

[IJabz]

Add support for PERFORMER field for ID3. ID3 already stores performer with their instrument in IPLS (Involved People list - ID323) and dedicated TMCL frame (Musician Credits ID3V24). Trouble is this field is not well supported, DbPoweramp discards it when transcoding files and MinimServer does not read it.

We already have a PERFORMER_NAME field (implemented as a TXXX frame) and used to store just the performer name. I think a PERFORMER field that worked the same as OggVorbis field (performername (instrument))would be good, with the existing PERFORMER field renamed to something like MUSICIAN_CREDITS.

However this could be confusing since only ID3 needs two fields.no other format and IPLS/TMCL is the official 'correct' field to use for performers

[IJabz]

Done.