Updating permitted data licenses

[afrubin]

The MaveDB project is committed to open data, so we should only allow open data licenses. This excludes the old default (and current option) CC-BY-NC-SA license.

A full list of open licenses can be found here.

It makes sense for us to stick with Creative Commons options, since we are licensing the individual records rather than the whole database. The available options after this update should be:

• CC0 1.0 link - default
• CC-BY 4.0 link
• CC-BY-SA 4.0 link

Note this also means we should remove the "other" option, although it's fine to retain the data usage requirements text box.

[afrubin]

We still have a couple of datasets using the old CC-BY-NC-SA 4.0 license and will have to decide what to do with these. I will attempt to recontact the authors and see if they're OK with us relicensing to one of the open licenses.

[bencap]

Other licenses can remain in the DB, but should not be selectable (via API or UI).