ACTN-172 - jin - adding an interface to add query string
ACTN-172 - jin - adding encoding for url
ACTN-172 - jin - using NSURLComponents to add query strings
ACTN-172 - jin - adding logging for error. Also, added return when input value or field for query string doesn't exist
Merge pull request #43 from lumoslabs/jin/existing-user-api-call-for-split-tests

Reviewed by Pat and Jesse