GUI JSON parse - provide callback to allow updating link URLs from development to production servers

[PatrickRyanMS]

It's reasonable to expect that any GUI created with the GUI editor in development may need to have assets migrated from a development server to a production server when it is taken live. Right now, the only path is to manually update the URLs for assets in the GUI Editor. It would be helpful to be able to update the server in the URL on a callback on the parse. We should also keep in mind that there are some applications that may also need to update the suffix of the URL such as in the case of Dropbox links which require an rlkey value. This may need to be added or deleted so being able to update the URL string as needed in a callback will give the most flexibility.