Add support for multiple curators to be recorded

[gaurav]

Since ORCIDs are the best way to track scholarly contributions, we should record the ORCIDs for curators.

This issue used to cover authenticating using ORCID's Public API. However, the main benefit for signing in using ORCID is just to confirm that contributor's ORCID, which seems unnecessary. Instead, we should:

1. Ask curators to authenticate with Github (Allow PHYX files to be directly uploaded to the Clade Ontology in Github #29).
2. On their first login, we ask curators for their ORCID and record that in a JSON file in Github repository that stores curated PHYX files.
3. When viewing a PHYX file from the curated repository, we prepare a list of contributors by getting a list of all Github users who contributed to that file and then looking up their ORCID IDs from the JSON file. While we'll miss contributors who made changes directly through Github, we can always modify the JSON file to include them.

[gaurav]

In retrospect, this issue was overly complicated and also unnecessary -- authenticating with ORCID doesn't give us any additional benefits, but authenticating with Github would allow us to create and update files directly from the Curation Tool (as per #29). I updated this issue to reflect this.

[gaurav]

Klados currently records:

• A curator name (in the curator field in the top-level Phyx object)
• A curator e-mail address (in the curatorEmail field)
• A curator ORCID (in the curatorORCID field)

None of these fields are currently included in the Phyx specification, which instead provides a top-level citation field that is intended to be a citation to the ORCID file itself.

Proposed changes

1. Remove these three individual fields and replace them with a single Citation that is described as the "Citation to this Phyx file".
2. Add support for including author e-mail addresses and ORCIDs to the Citation object.