Add simple output option to command line arguments

Daid,

While working on getting slicing into Octoprint I thought I could add something simple to Cura that would make integrating with it from the command line easier. If you don't want this patch then I'll have to write something that parses the output form calling Cura from the command line and then re-copies the file (which I'd prefer not to do but can if needed). Let me know.