Backport XenopusJamboreeParser from ensembl-xref

Created by: mkszuba

Description

Port changes made to XenopusJamboreeParser in ensembl-xref, including unit tests, back to ensembl:feature/xref_sprint.

Use case

See ENSCORESW-3223. Originally worked on by Prem.

Benefits

Salvage more work from the 2018 xref sprint.

Possible Drawbacks

Increased test-suite run time (note: Travis does not automatically execute tests from misc-scripts/xref_mapping yet).

Testing

Have you added/modified unit tests to test the changes?

Yes.

If so, do the tests pass/fail?

They pass.

Have you run the entire test suite and no regression was detected?

Yes (including tests from misc-scripts/xref_mapping), no regression detected.