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.
Several reasons:
* This previously looked horribly inconsistent.
* The Gtk selector was broken for plugins with many presets,
making it impossible to select presets. For whatever reason,
the use of a menu fixes this bug.
* Towards a hierarchical menu for banked presets.