Changed addJsonToPayload to void method
Outputs any error to the log, then returns out. This can be done better to let the caller know if there was a success or failure.
Fixed addJsonToPayload to encode the NSData object directly
 - Removed 3PD lib for base64encoding to use deprecated native library
(iOS 7 and lower)
 - Added addJsonStringToPayload for ease-of-use in the future (can be
removed if needed)
More tests for addJsonToPayload & addJsonStringToPayload
Specifically, tests for b64 encoding/decoding