Move group management to CLI. Bug 844415

This is just a chunk of bug 844415 but that bug is arguably too big anyway.  This moves adding and removing users+groups to the CLI. I started writing unit tests for this, but we're talking about a single .create() or .delete() which is all a part of the ORM anyway.  In a world where we wait 20 minutes for tests to finish this feels like one of those times when tests are unnecessary.  Your call.

r? @muffinresearch at least since he owns the bug, but anyone is welcome.