Write more tests, update OneToManyField

Write some tests for paths `architectures` and `architectures/:id`. As in the previous tests I've written, these tests are fairly basic: they check whether it's possible to GET each path, whether authentication is performed, and whether it's possible to create and delete the relevant entity.

Update `OneToManyField` so that recursive creates will succeed when one of these fields is encountered.

Following this commit, I'm going to try to whip up some data-driven tests that batter numerous URLs at once. If that succeeds, I'll trim down the test modules I've written.