Refactoring of appveyor script
Refactoring of appveyor script

Here we now do
 - Use ninja for build
 - use miniconda for getting most of the dependencies

It should be straight forward to also implement building
the internal python bindings later.

DLR-SC/tigl,DLR-SC/tigl,DLR-SC/tigl,DLR-SC/tigl,DLR-SC/tigl,DLR-SC/tigl