Faulty error message: The %license-name license is not enabled

When I encountered the following error, it wasn't very helpful:
The %license-name license is not enabled

The attached patch fixes this by outputting the actual license name. The simplest part was to use @license-name instead; no placeholder theming is necessary because it's a plaintext error message. I noticed that same string was created in three places, so to help avoid future bugs and maintain consistency, I made a single method that is now called in each place.