[quantile regression project]  final modification. attempt to add multiprocessing. but results are not conclusive

[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] refactor simulations. add transformed coordinate to the quantile functions

[quantile regression project] refactor imports for quantile estimators. two fix: nb_obs=1 in GevSimulation.py and df_merged correspond to df_coordinates from now on (such as it takes into account the transformation if there is one)