Add ORCID field in creators object [add-fields]

[mvolz]

Requested in the google group here: https://groups.google.com/forum/#!topic/zotero-dev/w72hVK-bK9M

I think this would be a great idea. The ORCID field isn't available in the wild very many places yet, but CrossRef has started to include it, i.e. http://api.crossref.org/works/10.1111/1365-2745.12293

[denismaier]

@bwiernik Can we add the Zotero label?
CSL related changes could be considered together in the context of the name data model revision.