Add Bayes Factor to Bayesian analysis

[rjjfox]

Investigate and potentially add a Bayes Factor score to the Bayesian approach.

This will allow people to refer to a table that indicates how strong is the evidence towards A or B being the better experience.

Concerns are that this will become a kind of 'threshold' that people feel they need to meet. This leads to a more frequentist way of thinking.

Bayes Factor information