Adding new `all=True` param to our `groups_required` decorator.

This will allow users to specify whether or not they want to force users to be a
member of every group, or just one.
Adding tests to assert that the new `all` param works.
Modifying our groups_required decorator.

It now handles:

- Objects.
- hrefs
- names
- An all param, which lets you assert whether a user is in one group, or many.