Copyright-holder and year information is extracted from git log.
git history begins in 2005. So (C) from 1998..2005 is lost. Also some
(C) assignment of commits where the committer didn't use --author.
Use RegionSelection for MIDI regions as well, since the old dumb stub didn't do
some things correctly. There's probably no reason to have a separate class for
this at all, and some good ones for putting all regions in the same selection,
so we should probably do that. For now they are still separate in the
selection but use the same base class.