Hook up BFGS to rest

********* PEOPLE *************
Primary reviewer: @sc932 

Reviewers: @suntzu86 

********* DESCRIPTION **************
Branch Name: denizokt_285_qei_rest
Ticket(s)/Issue(s): Closes #285 

********* TESTING DONE *************
don't raise bare exceptions and don't raise exceptions that don't have an error message. e.g.,
```
raise RuntimeError('some message here, you can print values too {0:.18E}'.format(value))
```