[GEV TREND TEST] rename and refactor the code for one parameter gev trend test (to prepare the introduction of tests with two parameters)

[HYPERCUBE] refactor hypercube. add the fact that for the fast mode, massif names are sampled randomly for the fast mode. this enables to explore the change point test results under different viewpoint.

[SCM] add 3 consecutive nb_days as default argument. add this argument for SWE and SD. Also add a test to SCM study

[SCM][HYPERCUBE] Add multiprocessing by default for abstract study. re-activate test_SCM_study which are now fast enough. fix issue with total precipitation variable. AltitudeHypercubeVisualizer first visualization.

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