BUG: Use ontology terms for EBI investigation_type

Use the terms stored in the database and add a new argument, `new_investigation_type`, which is only relevant if the value passed in `investigation_type` is `Other`.

See issue #405.

NOT READY FOR MERGE - I couldn't run the tests in my system.
Since this is a list, probably better to do
```
self.assertEqual(self.ontology.user_defined_terms, ['Test Term'])
``