Support for ORCiD as OAuth provider

Tests have been left out since you need to be a paying member of ORCiD to obtain keys to the API. This is a highly nisched integration, so tests are not as crucial as towards for instance Facebook. The integration is used successfully in our reference system, with identical code but with sandbox urls (api.sandbox.orcid.com) instead of production (api.orcid.com).
For 1.6.0 in fact.