Test activity streams through API only

The activity streams tests were working by calling the activity streams
logic action functions to get user, package and group activity streams,
and to get activity details, and then checking that the results are the
same when the same request are made via the API.

Instead just test by always calling the API (which calls the logic
functions anyway).

It should also use the API when the tests need to do things like create,
update or delete packages, resources, groups, users, etc. Currently it
still calls the logic action functions directly to do these.

It also gets things from the model sometimes, which it could get from
the API.