Move primitive types into their own nuget package

Primitives, like System.Windows.Point should be moved into a standalone Nuget package. They shouldn't be tied to WPF.
System.Drawing.Primities exists as a reference point. This would allow usage outside WPF.

That way, it's possible to reference them from libraries without having to put `UseWPF` into the .csproj files (keeping them small, as e.g. test projects testing the algorithms apart form their UI implementation should be)