Add support for new DataCite JSON REST API

[tmorrell]

DataCite has a new JSON REST API, and this PR will add a new client for interacting with this API. At a minimum it will handle getting DOI metadata and all DOI minting functionality. The REST API will eventually replace the existing MDS API.

I've added in some tests that require a DataCite test password; these are marked so travis should still be happy.

I haven't finished building out tests, and there are a few more functions to write before this is ready for review.

[tmorrell]

This is ready for review. The commits are a mess because I include both the 4.2 and 4.3 PRs. I'll rebase once those are approved. I also don't know why the travis 2.7 build is failing; seems like a really early configuration step.

This JSON API follows the same structure as the MDS wrapper, but I added a lot more helper functions for common DOI operations.

New files to look at: https://github.com/caltechlibrary/datacite/blob/rest-api/datacite/rest_client.py https://github.com/caltechlibrary/datacite/blob/rest-api/tests/test_rest.py

I've added tests that make DOIs in the DataCite test system, but that don't run on travis. Set the following environment variables $DATACITE_USER, $DATACITE_PW, $DATACITE_PREFIX with your account information for doi.test.datacite.org and run ./run-tests-pw.sh

Three tests will fail because DataCite hasn't implemented geoLocationPolygon yet https://github.com/datacite/lupo/issues/327

Feedback is much appreciated!

[tmorrell]

I've verified that the live DataCite tests still pass. The records with geoLocationPolygon metadata don't fail anymore, but the polygon metadata isn't included because DataCite hasn't implemented that field yet.