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

[COORDINATE] refactor starting year & df_temporal_coordinates. to normalize the same way any temporal covariate. So that each fit has the same type of normalized data as input. add multiple transformation.

[MAX STABLE] add starting point for non stationary full estimator. fix display in non stationary trends

[EXTREME ESTIMATOR][MARGIN MODEL] add ismev gev fit. and refactor. add result_from_fit abstract class.

[EXTREME ESTIMATOR][MARGIN MODEL] add stationary/non-stationary margin model. fix margin formula (in the temporal case when we want a dependency on a single parameter for instance). add margin function with starting point