Fix project licensing issues

* Use valid [License SPDX Code](https://spdx.org/licenses/) for package.json
* Set the missing `url` name and value to point to our LICENSE
* Include short text for GPL-3.0+ instead of full with proper copyright and attribute to the project
* In the short text rewrite *(extend)* url to point to full GPL-3.0+ text [found on GNU](http://www.gnu.org/licenses/gpl.txt) ... they aren't going away anytime soon.

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Only things to discuss is if you @sizzlemctwizzle want to do any of the following:

* Include the full GPL text in the project as `./LICENSE.gpl` but keep `./LICENSE` since it contains the actual Copyright notice.
* Change the Copyright notice in `./LICENSE` to [members only url](https://github.com/orgs/OpenUserJs/members) or [keep the existing teams url](https://github.com/orgs/OpenUserJs/teams)... or optionally just you since you are the first commit and owner.
* Anything else you want me to do while I'm in here?

Tested in dev with current project head 84ccee2