Initial port of CCK Signup Group to 7.x

I just committed a working version of this sub-module. It still needs some work both on the admin UI (right now it has separate vertical tabs for just this module, instead of nesting below the main CCK Signup module's tab), and its performing an inefficient query to check the capacity (its using EntityFieldQuery, but it should do one single SUM query).

Done. As for the EFQ bit, this module is now using a normal db_select, so it won't work with group count fields stored in non-SQL storage.

Still needs #1049408: Port group fieldgroup functionality to 7.x.

Now works with field_group module.