[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] remove run time error and no trend from trend plot. add Altitude_Hypercube_Year_Visualizer as an extension of Altitude_Hypercube_Visualizer

[SCM][HYPERCUBE] improve labelling of all the graphs. add test strength display in the spatial case.

[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][HYPERCUBE] Add multiprocessing when loading abstract study. Refactor abstract variable and all variables accordinlgly.

[SCM][NON STATIONARY TREND] modify some display parameter. add pre loaded LATITUDE & LONGITUDE to scm_constants file. remove massif file.

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