Mark lots of tests as skipped if they required plotting or the net

Lots of skipped tests won't pass at the moment, that needs to be
resolved, but I'm not sure how many of the tests are useful. Also I need
to add some nice test data to the repo and use get_test_resource()
everywhere.
Test User.from_rk
Add method User.to_rk()
Make it possible for anyone to run ORM tests
Relate Tracks to Users
Handle reimporting of tracks