Added Bandit BLA implmentation

********* PEOPLE *************
Primary reviewer: @sc932 

Reviewers: @suntzu86 

********* DESCRIPTION **************
Branch Name: norases_373_bla_bandit
Ticket(s)/Issue(s): Closes #373 

********* TESTING DONE *************
make test
make style-test

Bug fixed:
variance in a sample arm is dropped in _make_bandit_historical_info_from_params
Oh right we'd have to figure out how to use deferred schema bindings in colander or write custom validation code to handle the different validation cases. I guess it's not a huge deal right now while there are relatively few bandits. But there's definitely a lot of duplicate code. I guess punt on this