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
do you have any intuition from testing or guides to link to or whatever describing what this stuff does? where did your suggested defaults come from? presumably rhobeg/end should depend on the length scales of the problem.