Omniauth makes it very easy to add more authentication options. We should add ORCID (which now offers OAuth2 authentication for non-members) and Github (for developers).
adding github and orcid as authentication options. Closes #196
make email column in users model optional. #196
added modified omniauth-orcid gem. #196
allow ORCID admin users to add email address #196
added tests for authentication. #196