This can handle non-const -> const constructions and assignments. Due to
the automatically generated copy- and move-constructors and assignment
operators, some SFINAE tricks and little code duplication are needed to
make it work.

The compiler itself takes care of the problem by doing the right thing
in the problematic methods and not allowing to modify the
const-qualified data.

This is technically not necessary, but hides about 5 MB of compiler
warnings :-D

I think this is much better because even operators inherit from Domain
and operator.getDimensions() is very confusing.