Added Bandit UCB1-tuned implementation

********* PEOPLE *************
Primary reviewer: @sc932 

Reviewers: @suntzu86 

********* DESCRIPTION **************
Branch Name: norases_366_ucb1_tuned_bandit
Ticket(s)/Issue(s): #366  

********* TESTING DONE *************
make test
make style-test
variance = 0 means variance is zero (e.g., always wins). variance=None is let us compute variance using Bernoulli RV formula variance = p(1-p).