Adds order to the test models to make the results more predictable.

Even though there was some code in place to prevent results in random order from PostgreSQL we were still experiencing this with Jenkins and Travis.

This commit removes the old code that handled this. From now on this will be handled differently. Every test model will order by its primary key. You can disable this by changing the order property of the model to `null`: `$testModel->order = null`.

All those `$model->order = null` are necessary so that the tests can remain the same.