Improve test script

Now the validity of the local NeuroML definitions (as LEMS files) and of the local NeuroML examples (as NeuroML files, as defined by the local schema files) are checked with actual unit tests using nose.

Issues with the consistency of the copies of these files that other repos should have, or with jnml not being able to validate the NeuroML examples, are still reported, but they don't break any test as they don't really concern this repo.