Enable contributor provided "Additional Themes"

[aclayton555]

This ticket emerges from https://sagebionetworks.jira.com/browse/CPO-1009

TL; DR - Themes in the CCKP are associated with grants. Themes on research outputs (e.g. publications) are inherited from the parent grant. With the shift toward community curation, can contributors add additional themes to their resources? If we did not want contributors to make changes to the grant-inherited themes, then we could consider implementing an “Additional themes” attribute that was free-text for contributors.