[projection snowfall] modify altitude_class to altitude_group in visualizer_for_projection_ensemble.py. fix index for ensemble dataset.  add plot_relative_change_in_return_level.py

[contrasting] for preliminary_analysis.py from now we use fevd fit method & fit on series with more than 90% of non zero maxima. improve coherence plot

[contrasting] add pointwise_gev_study_visualizer.py and add confidence interval for the gev parameters for is_mev fit method

[contrasting project] add test for study loader. refactor their init function to have a better error message.