tweak(cgit): better defaults & fix vestigial refs
tweak(cgit): better defaults & fix vestigial refs

- Rename default reposDirectory from /srv/git/repos to /srv/git/public.
- Add default user to git group.
- Make repos directory group-writable.

hlissner/dotfiles,hlissner/dotfiles,hlissner/dotfiles,hlissner/dotfiles,hlissner/dotfiles