Investigate possibility to remove the XML header

Investigate other options for the XML header currently used in the Behavior API. Customer has reported that it's a bit inconvenient to have this separate header that defines the UI for the Behavior script as it can easily be out of synch with the script code that is then underneath the header. They'd prefer a more "in-line" approach for defining the UI for the script.

Investigate what other options there would be in QML to expose the UI elements for the script. Perhaps a special QML element could be used etc.? This of course means we'd need to also re-implement the loader for scripts and if the behavior scripts are changed. Perhaps same mechanism needs to be applied to custom shaders as well to keep the implementations in synch.