Add a Creative Commons License picker in attribution options

[SaraJL]

When adding attribution information to media in StoryMaps, it would be nice to have some type of license picker that populates Creative Commons licenses. Currenty, when citing media I tell clients to copy/paste the license at the end of the attribution:

If there was a dropdown/picker as another option in this window to select a license, it would help promote a consistent format for users. It would also make it a lot easier to be able to auto-add a license.