Asset dual licensing

This infrastructure proposal explores the pros and cons of dual licensing for assets.

Asset licensing in theory
In theory, all assets are preferably dual licensed under CC BY-SA 3.0 & GPL 3.0, according to the License article.

Status quo in reality
In reality however, all assets that can be found in SVN right now are just single licensed under CC BY-SA 3.0, according to their .license file.