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
it'd be better to define a utility somewhere and call it. b/c in principle you can pass a cpp_wrappers domain around and it would work. but if you want to have this fail with "not implemented" that'd be fine too