Track git commit author based on logged in user if user name and email are available.

Add a "(via akcode)" suffix to commit messages so that commit-hook systems can review
the commit message to distinguish between a direct git commit (which must be pushed back
to akcode) and an akcode commit (which must not be pushed back to akcode)

Some systems can use the changeset's committer information instead, but Trac doesn't seem
to know how to get that information in a RepositoryChangeListener component.