Automatic testing for consistency between nidm-results.owl and examples

This pull request includes:
- A test class to check that examples in the `nidm-results` directory complies with `nidm-results.owl` (check class names and attributes domain): `TestExamplesMatchVocabulary.py` .
- Travis CI configuration files to automatically run this test when new code is pushed to incf-nidash/nidm repository (using  as discussed in #106).
- Various fixes to insure the consistency of the `provn` examples and `nidm-results.owl` file.