Added Bandit epsilon-greedy implementation

********* PEOPLE *************
Primary reviewer: @sc932

Reviewers: @suntzu86

********* DESCRIPTION **************
Branch Name: norases_255_create_epsilon_greedy_bandits
Ticket(s)/Issue(s): Closes #255 

********* TESTING DONE *************
make test-no-tox
make style-test-no-tox
Updated description: Implementation of the constructor of Epsilon. Abstract method allocate_arms implemented in subclass.

I think Epsilon is ok because we are under bandit folder. moe.bandit.Epsilon is clear. I am trying to avoid