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.
metagenomics is actually an actual ENA ontology time, so not an other investigation type. See [example study xml comments section (at bottom)](http://www.ebi.ac.uk/ena/submit/preparing-xmls#study)