This should be hidden in the UI as well, but the backend should support this too.
We also want to set initial rating of 1 for contents that need it.
This commit includes a new unittest for this case.
Reviewers: sybren
Differential Revision: https://developer.blender.org/D2825
Refactor of pillar-server and pillar-web into a single python package. This
simplifies the overall architecture of pillar applications.
Special thanks @sybren and @venomgfx
