Move setting up orm to orm files

2 methods were added: to set up and teardown ORM specific things in tests.
All ORMs can now override these empty methods.
remove space between negation and condition
Remove DataMapper-specific code from tests

I've checked the DM-specific code and most of it was possible to remove without
any problems. There's however an issue that sometimes the class needs to be
finalized after manipulating its structure. Therefore a new method was added to
internal helpers "udpate_model", which will just execute block for other ORMs,
but in DM will also finalize the class
Solve loading order issue for tests (MongoMapper)
Merge pull request #570 from arnvald/remove_orm_coupling_from_tests

Remove orm coupling from tests