Default behavior check

[serk12]

Added ScenePlugin::defaultBehavior to know if a plugin should be True/False or just ignored as a default behavior.
Also, roll back in the previous try.

This is related to: OpenChemistry/avogadroapp#235

Signed-off-by: Marc Prat Masó marc.prat.maso@estudiantat.upc.edu

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[github-actions]

Here are the build results
Avogadro2.AppImage
macOS.dmg
Ubuntu-2004.tar.gz
Win64.exe
Artifacts will only be retained for 90 days.

[ghutchis]

Yes, I think this is a much better idea.