Template type deduced operator+ and - added
Template type deduced operator+ and - added

The old operator+ only allowed for int additions.
the `Wpedantic` warning flag throws an error over
this. Added a template type deduced operator+/-
that performs a `static_cast` to a `double`.
This should enable the use of all arithmetic types
with AngleDegrees for the + and - operator.

Ultimaker/CuraEngine,Ultimaker/CuraEngine