*The narrowui value was hard coded in all ui scripts, made an user preferences option. Basically this value determines on which area width, it should switch between dual/single column layout.
ToDo: The Changes only take effect when reloading scripts/restarting Blender (after saving as default). Will maybe add the "Reload Scripts" operator next to the button in the future.
* Small fix for Fluid Add Button, when in single column mode. Didn't expand like the other "Add" Buttons.
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