Let SceneTreeDock duplicate nodes via Node::duplicate()

[RandomShaper]

A small logic fix is included as a separate commit, since that should be done regardless the code was to be unified or not.

This is implemented on top of #13040, so it should be merged after it. That one already merged. This one rebased against current _master-.

Helps with #11182.

[reduz]

So, whats going on with the Undo/Redo for all this?

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On Sun, Nov 19, 2017 at 8:12 PM, Rémi Verschelde ***@***.***> wrote: ***@***.**** approved this pull request. — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#13041 (review)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AF-Z248HPzJFi2AW72ksUMU7C-LFwTxCks5s4LXvgaJpZM4QjZPJ> .

[RandomShaper]

The only thing thas SceneTreeDock::duplicate() had in relation to undo/redo was the "duplimap" and it is now collected at Node::_duplicate() when running in the special editor mode (called through Node::duplicate_from_editor()).

[RandomShaper]

I've done my best to transfer to Node::_duplicate() all the logic differences present in SceneTreeDock::_duplicate() with special tools-only flags.