Add getter functions?

I know we have the setFeature and getFeature functions, but we also have a setResolution function but no getResoultion.

I think it would be a good addition to add these getter-type functions. The changes should be rather easy, as we can just register the setter-functions with None inputs in the camera template class.

What do you guys think? @kroeger @melchert @quentin

This change should not break any code, but allows to be a bit more flexible and "obvious" when requested a special parameter.