Produce a Babel variant that uses level 0 of the UMLS

[gaurav]

The UMLS licensing agreement is at https://uts.nlm.nih.gov/uts/assets/LicenseAgreement.pdf. The UMLS precomputed subsets page refers to the “UMLS Metathesaurus Level 0 Subset”, which I think corresponds to “Category 0" on Appendix 1 (page 4) of the license agreement: “general terms of the License apply with no additional restrictions”. I'm not sure if the Translator licensing agreement that allows us to use UMLS allows us to (1) share any data outside of Translator at all, and (2) if so, whether we're only allowed to share Category 0 data or all available data. But we should figure this out before we publish Babel.