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.
A Gtk::manage()d widget will be deleted when its parent container
is destroyed. Top-level context menus are not inside a container and
hence need to be manually deallocated.
This adds explicit delete calls for menus where there is a
member variable reference to the Menu.
