Recommended content algorithms

[mattosborn]

We need to design the algorithms for surfacing content in a few places

1. The in-line recommended pages ("you may also like") widget
2. Chapters on the home page
3. Case studies on the home page
4. The ordering of content on the collection pages:
   • Topic tag pages
   • Stage tag pages
   • User tag pages
   • Author pages
   • Search pages (this is already implemented but may need some testing and tweaking

It may be that each of these has a different approach. Ideally we would do all of them in a way that doesn't involve any user data, as this will make the implementation simpler.