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
For request, I think we cannot generalize any further due to defaults and sample request. We should keep each request easy to understand to users.

I am not sure if we can do that for views. I already have BanditPrettyView (inherits from PrettyView). I can generalize the bandit_x_view function but that requires adding this complication of a constant BANDIT_TYPE_TO_SUBTYPES_TO_BANDIT_METHODS. Or is there a better way to do this?