8 add tests to api

## Adding tests for the API
This is in preparation for re-factoring some parts of the API, see issue #8 for more information.
*Note to reviewer*: As usual there are some Django magic and also some Tastypie (rest framework) specific things going on here. Let me know if you want more comments to explain this.
 
Reviewer: @joachimmetz
Suggestion: personally I would have the defined the function as:
def _test_get_resources(self, request_data, expected_keys):

and have every implementation pass them as args instead of relying on the current naming convention.