[quantile regression project] add test exp simulations (stationary and non stationary) for models on annual maxima. Prepare the code to fit with non stationary exponential models

[quantile regression project] add annual maxima osbervation from daily exponential. add sammple_r_function as argument to rmargin_from_nb_obs. add abstract extreme params

[EXTREME ESTIMATOR] refactor margin_fits folder. extreme estimator folder. and extreme_models folder

[GEV] add computation of the mean & variance. modify gev_estimator. add function visualize_summary_of_annual_values_and_stationary_gev_fit: to quickly visualize the repartition of the main empirical indicators and corresponding stationary gev indicators.

[SCM] improve empirical distribution visualization for slides. add single_massif_graph visualization

[EXTREME ESTIMATOR] add margin_fits folder. add gpd params & gpdmle_fit. refactor code to handle gev and gpd together