Turn this in to a FreeCAD Preference Pack

[luzpaz]

See https://github.com/Chrismettal/FreeCAD-Behave-Dark-Preference-Pack

Edit: FreeCAD-Behave was added to the Addon Manager (see FreeCAD/FreeCAD-addons@0d23295)

ref: FreeCAD/Addons#16

[luzpaz]

@OBKF would you have any time to do this before we release v0.20 (in a week or 2) ?

[luzpaz]

bump

[luzpaz]

bumpity-bump