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
why call get explicitly vs using ``[]``?

also, if you need a default value, you can ``sampled_arm.get('loss', 0.0)``