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
this already complicates historicaldata b/c it has to know whether or not you have a Bernoulli arm.

BernoulliArm could be a subclass of SampleArm. override init and validate to do whatever special things and call the superclass

@sc932 any ideas?