Keystone v3 improvements.

Managers for project group membership, project user membership, project combined membership (users and groups); for group project membership, group users, group roles; for user project membership, user roles.
The focus of js-openclient if to try and make the most usable client regardless of the API's structure. As such, it would be nice if this meta-manager was capable of doing a GET for either a user or a group. I'll accept a TODO for now. :-)