Merge util/export_website_groups.py into groups/format_groups.py

[adehnert]

util/export_website_groups.py does something very similar to what groups/format_groups.py. It's a separate script right now because (a) history and (b) it uses Django templates, not Python string interpolation. It'd be nice to merge the two, which probably involves adding Django template support to groups/format_groups.py. (As a bonus, this would probably make fixing #174 automatically add a web UI for util/export_website_groups.py's output.