Determine public domain status of less commonly used licenses in 'spdx_licenses'

[trevorld]

• To help with auto-guessing xmpRights:Marked (a field Creative Commons recommends setting #23)
• Lots of licenses, for now don't read through all of them but just do a few of the bigger ones
• FALSE if public domain, TRUE if not public domain, NA if unknown

[trevorld]

• A pd column was added and we've determined TRUE or FALSE for the more popular open source licenses including all Creative Commons licenses.
• Still a lot of licenses that are still NA...