Add CC licenses

Adds a rudementary license selector for new prisms
Updates old prisms to public domain
Adds license icon on prism#highlight and prism#visualize pages

references #195
Merge branch 'develop' of github.com:scholarslab/prism into develop
Fixes tests

Updates tests to use 'Prism' object rather than the 'Document' object
Adds factories for a default Prism and one that is unlisted
Moves view specs for documents to prisms
Removes marking spec