[3d] add show labels toggle, default to off

[nirvn]

Description

@wonder-sk , you give me a working mouse pan, I give you a label toggle setting 😉

Newly-added setting is found right here:

Checklist

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[wonder-sk]

Looks great! Just one detail, could you add support for this flag also to readXml/writeXml methods? They are not used right now, but they will be soon :-)

[nirvn]

@wonder-sk , done. Thanks for the swift review.