This MR enables almost all known compiler warnings and treats them as errors. This should help maintaining a high code quality.
I fixed the errors currently occurring. Since some where shadowed variables and shady casts, we should check with different data sets (ATLASpix, TPX3, CLICpix2) that everything still works as expected.
This currently fixes all Clang errors, some more reported by GCC still need to be tackled - that's why the compilation is failing currently.