Moved bandit policies into sub directories

********* PEOPLE *************
Primary reviewer: @suntzu86 

Reviewers:

********* DESCRIPTION **************
Branch Name: sclark_375_move_bandits_into_folders
Ticket(s)/Issue(s): Closes #375 

********* TESTING DONE *************
tested gui
make test
make style-test
we usually list out subfolders (i.e., packages). even just simple ones like "moe.bandit.bla: the BLA family of bandit polices" or whatever