Update /git-repository-usage-policy to allow "GPL friendly" licensed non-code assets

I'm not sure this belongs in this queue, but @webchick suggested we open an issue in #2916161: License considerations for the Out of the box initiative so here it is. Without rehashing the entire history of this request, the spirit of these changes have been thoroughly vetted by the Licensing Working Group (LWG) and proposed to the DA twice (first under Holly and again under Megan).

The goal of the changes are very specific. The LWG has suggested that the DA alter the current Drupal.org Git Policy from requiring EVERYTHING that is committed be licensed as GPL-2.0 and later to only requiring original work that isn't already licensed another way use this license. The LWG would like to start approving expectation requests for non-code assets that use appropriate "GPL friendly" licenses for the type of asset like Create Commons Share Alike by Attribution CC-SA-BY for text or the SIL OFL for fonts.

The Licensing Working Group will maintain a list of allowed licenses. While not all approved licenses will be truly GPL compatible, the LWG will only approve licenses that protect 4 essential freedoms so developers will still be able to use, alter, and share what's downloaded from Drupal.org they way they always have under the strict GPL compatiblity version fo the policy.

The process the LWG will use to grant an exception for a non-code asset will be:

1. Is the requested exception code or a non-code asset?
2. If it's a non-code asset (font, image, text), does is it use an approved licenses?
3. If it's a non-code asset using an approved licenses, the LWG will approve the request.
4. Once developer commits the asset approved by the exception, the LWG will confirm that only the asset that was granted with a process similar to how we vet the repos for whiltelist request for additional code or assets using an unapproved license
5. The LWG will also confirm that provenance, license, and source for each exception is documented in the project. Developers can use the recommended ASSET.yml file like http://cgit.drupalcode.org/user_guide/tree/ASSETS.yml or a less formal markdown document found in many projects on GitHub.
6. Finally, a member of the LWG will close the Exception Request issue

The LWG won't police projects for licensing violation, but will respond to reports of licensing issue like the license of a previously approved asset changing to a less GPL friendly license.

The Drupal.org Git Policy is a really dated document with plenty of typos, grammer issues, and confusing sentences. As much as possible, we've refrained from altering anything other than the parts of the document that relate to licensing.

PLEASE. If you are looking at this policy for the first time since agreeing to it (everyone with a git account agreed to this or the CVS version of it), PLEASE not to try to rewrite the entire document. Again, there are dozens of issues that have been postponed for years because we haven't been able to get the licensing changes approved by the DA.

PLEASE do not derail this request by bringing up other licensing related changes that could be made or hypothetical edge cases. This change is focussed specifically on non-code assets and clarifying other parts of the Git policy that frequently confuse members of the Drupal community.

The strict GPL-2.0+ compatiblity requirement has served the Drupal project well over the years, but it's time to adjust to the fact that off our island GPL isn't the standard for creative works develoeprs would like to include in their projects.

https://docs.google.com/document/d/1zk3ugQbzYwbg5PeYMJvLzUczS-zqHnif-0if...