allows experiments to periodically use the Bayesian bandit calculations to rebalance the distribution of probability of each alternative in the split test

Conflicts:
	lib/vanity/adapters/abstract_adapter.rb
	lib/vanity/experiment/ab_test.rb
	test/experiment/ab_test.rb
Merge pull request #154 from assaf/feature/bayesian_assignment_probabilities

Bayesian assignment probabilities