Data -> Hex string utilities

[ateliercw]

Add the ability to dump a hexadecimal encoded version of a "Data" object to make up for the fact that Data no longer returns a hex string as the description.

Useful for apps that needs to send push notification tokens up to the server

Potential approaches are documented here: http://stackoverflow.com/questions/7520615/how-to-convert-an-nsdata-into-an-nsstring-hex-string/7520655#7520655