Hydro final lvl (CR 25) to merge in develop

[guilpier-code]

This PR attempts some code enhancements on branch feature/final-reservoir-level-cr25. Therefore, this PR's associated branch (fix/hydro-final-levels-cr25--try-fixes) is based on feature/final-reservoir-level-cr25.

• [x] in class FinalLevelInflowsModifier,
  • try to reduce the number of data members,
  • making data members private whenever it's possible,
  • define a clear interface with a smallest number of public functions
  • and so make the more methods private as possible
• [x] Unit tests : clarify their intention and reduce their size
• [ ] caution : could not remove yet the initialize method. This method should be merged with the constructor, but when we call the constructor, all input pieces of data are not available. that's why initialize exists. We should try to make these pieces of data available, for instance by changing the order of data loading

For any purpose, here are doc resources :

• specs here
• a discussion on that matter here