Add mEDRA DOI search translator

This one is actually not bad (besides requiring cross-origin `processDocuments` calls). Tried to clean up the metadata as much as I could and it's working quite well. Tested with a couple dozen DOIs, but probably not very exhaustive.

Scrapes metadata from pages like this: https://www.medra.org/servlet/view?lang=en&doi=10.12851/EESJ201312ART13

Priority places this just ahead of Airiti and behind DataCite.