Closescoder/internal#168
Gets rid of the "global state" authentication, and adds a `login` helper
which should be called at the beginning of each test. This means that
not every test needs to authenticated as admin, and we can even have
tests that encompass multiple permission levels.
We also now create more than just the single admin user during setup, so
that we can have a set of users to pick from as appropriate.
ケイラ