Change name to Steppers-> Optimisers and move them to a separate section. Use warning/info/error messages.
Created by: gcarleo
This pull request mainly moves Stepper
into a dedicate section, to be logically consistent with other input sections.
It also introduces info/warning/error messages utilities, to be used in place of existing output messages. The goal is to have more compact expressions, without explicitly calling MPI primitives in all the classes where messages are needed.