Fix false error detection in the Replay Gain tool

Conflicts:
	src/CHANGELOG
Adjust gain for mp3 files
Fall-back from album artist to artist in "meta data" naming mode if album artist is empty
Add option to copy files instead of re-encoding them if input and output codec are the same
Properly re-paint conversion file list on status change
Fix status label
Merge branch 'fixes-2.1'

Conflicts:
	src/CHANGELOG