added COBYLA (no REST interface yet)

********* PEOPLE *************
Primary reviewer: @sc932 

Reviewers: @suntzu86 

********* DESCRIPTION **************
Branch Name: denizokt_370_constraints
Ticket(s)/Issue(s): Closes #370 

********* TESTING DONE *************
make test
make style-test
hmm i don't have too much intuition, especially for what rhobeg is. but i do know that rhoend best corresponds with the end result accuracy.

the suggested values are from scipy docs.