Added Bandit BLA implmentation

********* PEOPLE *************
Primary reviewer: @sc932 

Reviewers: @suntzu86 

********* DESCRIPTION **************
Branch Name: norases_373_bla_bandit
Ticket(s)/Issue(s): #373 

********* TESTING DONE *************
make test
make style-test

Bug fixed:
variance in a sample arm is dropped in _make_bandit_historical_info_from_params
potentially one more reason to differentiate btwn bernoulli and sample arms. not specifying 'loss' is invalid except for bernoulli arms right?