Allow setting license configuration in settings.json

[kevcube]

This way I can move my license with settings sync instead of being asked to enter it all the time.

[ImOnALampshade]

Just FYI, as a workaround, if you put the license GUID in a comment in your settings.json, the comments will sync! it doesn't prevent you from needing to enter the license, but it at least makes it slightly easier.