Merge Preferences into preset

[furti]

Now the Macro simply overrides the configuration files in a preset when called on an existing preset. It would be better to Show a diff of the preferences to the user and let the user choose what preferences to override and what preferences to ignore.

So it will be possible to start the default FreeCAD instance, change some common settings, and store them in all our presets.

[furti]

Check if we can use https://github.com/FreeCAD/FreeCAD/blob/be5e93ddfe29d49a4b1c02e7119b1f926549ccce/src/Base/ParameterPy.cpp to load the presets and compare them against each other.