Automatic User properties should be prefixed and documented

[cfjedimaster]

All properties set by default by Ionic on the User object should be both documented and prefixed. So for example, the system ID (used by Analytics) is set to _id. But there are multiple properties like device, is_on_device, and image, that should probably be renamed to something like _device, or perhaps

ionicMeta.device

The idea being to ensure my app doesn't accidentally conflict with something Ionic sets by default.

And of course - all these keys should be documented as to their purpose.