Improve artwork scoring method

[epii]

Use a Dirichlet smoothing method to generate an artwork's score, rather than a Wilson interval.

The Wilson interval has no defined value in the absence of any ratings and behaves poorly when there are only a few ratings (the score is too pessimistic).

See: http://masanjin.net/blog/how-to-rank-products-based-on-user-input

This is implemented by the dirichlet branch and just awaiting review.

[eevee]

There's also this post which I have had open in a tab for decades and would like to close: http://masanjin.net/blog/smoothing