[EXTREME ESTIMATOR][MARGIN MODEL] add temporal linear margin model test. check that starting point are taken into account.

[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

[SIMULATION] add simulation file to check issue that existed with respect to quantile gap in my last presentation

[SCM] improve visualization of the margin. add a 2D optional mask & visualization bounds to visualize a 2D margin

[SCM] add permutation which correspond to the sum of rainfall & snowfall. add test based on Durand paper.