(Partially) unbreak the test system

Our test system (on our current shipping branch) is a mess.
Dependencies are not even included, the wrong (obsolete) names
are referenced (in vain), stubs are missing. etc.

This PR takes care of some of the issues.

Our tests still fail, but now at least we have all the stub files where
we want them, and we are at least attempting to run most of the tests.

This is required so that I can add some tests for https://github.com/hypothesis/annotator/pull/92.