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

[EXTREME ESTIMATOR][MARGIN MODEL] refactor linear margin model folder organization. refactor names in univariate trend analysis

[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