Add CC-0 license information, based on RDF/XML

This is a BadgerFish conversion from this template:
```
<rdf:RDF xmlns:cc="http://creativecommons.org/ns#"
         xmlns:xhv="http://www.w3.org/1999/xhtml/vocab#"
         xmlns:dcterms="http://purl.org/dc/terms/">
  <rdf:Description rdf:about="http://opentreeoflife.org/curator/study/view/{STUDY_ID}">
     <cc:license rdf:resource="http://creativecommons.org/publicdomain/zero/1.0/"/>
     <xhv:license rdf:resource="http://creativecommons.org/licenses/by-nc-sa/3.0/"/>
     <dcterms:license rdf:resource="http://creativecommons.org/licenses/by-nc-sa/3.0/"/>
  </rdf:Description>
</rdf:RDF>
```
This is verbose, but it provides hooks for a few different
license-detection schemes.
Add test for CC-0. Add new study ID to license.
Merge pull request #68 from OpenTreeOfLife/internal-rdf-license

Record CC-0 license in NexSON as pseudo-RDF/XML