Add test for adding a record to a hasMany relational association

I named it `00_test_relational_associations.js` so that it comes first in the test suite. The reason for this is that the "Deleting records" test always [freezes for me](http://cl.ly/image/341g1w2Z3c0y).

I plan to write a test for the other end of the relationship and also for removing a record from a such relationship for which I already have some working code.