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
I agree we want to keep the requests as simple and easy to use as possible.

Having a linker from subtypes to methods could work, but feels hacky. I'd rather this be super clean. Idk if that means leaving as is, linkers, subclasses or what, but go with whatever is easiest to read and cleanest.