Update languge to embrace GPL "friendly" licenses

[kreynen]

These are mainly changes to make it clear that Backdrop projects do not have to be hosted in Backdrop Contrib and that GitHub.com doesn't have the same license requirements as Drupal.org. Users should be allowed to commit images, fonts, and code using licenses that allow the assets to be distributed within a GPLv2 project.

This goes back to https://www.drupal.org/node/1856762

While we are slowly making progress on getting past the GPLv2 only mindset for all assets some early Drupal contributors still cling to, there is no reason Backdrop should adhere to developer centric Drupal.org policies created ~10 years ago when disk space was a concern. What kind of modern, enterprise ready project makes statements like https://www.drupal.org/licensing/faq#q10

Doing so creates a fork of that 3rd party library, which makes it more difficult to maintain and only serves to waste disk space.

Requiring what is contributed to Backdrop Contrib to use a license that allows it to be distributed within a GPLv2 project rules out anything using an Apache2 license, but it makes it clear other GPL friendly licenses for non-code assets are allowed.

While Drupal modules like https://www.drupal.org/project/fontawesome add both a Drush .make and .inc to make it as easy as possible to install the required library while adhering to very a dated licensing policy, WordPress users can simply install https://wordpress.org/plugins/font-awesome/... which is hosted on https://github.com/rachelbaker/Font-Awesome-WordPress-Plugin... and has 48 forks.

WordPress's approach works better for both site builders and developers.

Unless https://github.com/backdrop-contrib has the same goal Drupal.org's contrib repo had for years... "everything you download from Drupal.org is GPLv2", please adopt language that embraces the fact that open licenses go beyond code and that an asset can be GPL friendly without being strictly GPLv2 compatible.

[quicksketch]

Thanks @kreynen! It all looks good to me!

We definitely do not have the same policy as Drupal.org that requires libraries be separately downloaded. I think it's expected that modules will bundle their libraries in most situations. Things might change once we figure out a consistent way to handle libraries (backdrop/backdrop-issues#159), but until then I think bundling libraries will work to solve most problems.

Merged the changes. Thanks for your attention to this!