Refactored api tests

Ok, I thing this is finally ready.
I verified it with pep8, there are two things it doesn't like:

First, method(**{"some":"magic"}), that I really like for writing data-driven tests :)

Second, I have ModelApi variable, that looks like a class, because it stores a class and I use it as a class.

I think I have achieved the perfect sweet-spot for writing simple crud tests for api,
basically I just need to define the entrypoint, generator for valid item, and path to id in result.

I already have 3 api points covered, I think I will have another dozen by tomorrow :)