Apply the structural changes to master branch, namely:
- The use of CoreState class as a container for core state quantities (implements #19 (closed))
- Depreciation of ComputationContext (closes #9 (closed)) in favour of ComputationConfig that only stores relevant parameters of the config files (no matrices)
- The use of Forecasts and Analyses classes that inherit from ComputationStep.
- Easy choice between Python and Fortran implementation for each step
- Python implementation is now the default one and wrappers were implemented (build_legacy...) to adapt to Fortran syntax rather than the other way around.