#906 Store node scripts in their own XML element rather than in user attributes

[Daniel Polansky]

(This is mainly for tracking/recording purposes.)

Ideally, when stored in a mind map node, scripts would not be stored in user attributes but rather in their own XML elements. One would have to add rename and delete functions to the script editor. Obvious downsides are introduction of file format incompatibility and changes. (Yes, I should have recorded this years later. Better late than never?)