Add ORCiD identifier to curation table

[cthoyt]

I think it's reasonable to say that when people make curations to the INDRA Database, they are doing so for the public good. Most biocuration efforts are moving towards more transparent models of attribution based around ORCiD identifiers.

Unlike email addresses, there is no issue with sharing information about people who made contributions to the INDRA Database if we do so using their ORCiD identifiers. If there's any debate about this, then I'd suggest we write a terms of service in which it's made explicit that if you register for an account on the INDRA database and then submit curations, your ORCiD identifier will be attached to that information and potentially be available for public download.

In practice, I'm not sure exactly how this would work. Maybe it means adding an orcid column to the Curation table?

https://github.com/indralab/indra_db/blob/1740fd2006dbee41324f4b5db3a75c3f88fbc8b8/indra_db/schemas/principal_schema.py#L984-L999

A side benefit of using the ORCiD identifier is that the code for appending a salt to the curator email and hashing it is no longer necessary when distributing curations in #187.

A second side benefit of using the ORCiD identifier is we can take advantage of APICURON as a tool for tracking curation efforts. We did this already for Biomappings (and interestingly, were the first external contributors).