[refactor] rename folders for one/two fold fit. move the code for the anomaly into temperature_covariate.py

[refactor] move altitudes_studies.py. create trend test folder inside extreme_trend. deactivate one test for param_function that was crashing globally for unknown reason (but locally the test is working).

[projections] add visualizer_for_sensitivity.py based on visualizer_for_projection_ensemble.py. add temperature_to_year.py file.
Fix max abs recurrent issue (when it was equal to zero). add one test for one fold fit, that was that due to a scale parameter that was close to zero, and was causing instabilities in the nllh value. This is fixed by changing the check for implausible in one fold fit, and by saying that if the scale parameter is close to zero then the parameter is undefined.

[projections] add mean merge function for the ensemble. fix max abs for median/mean visualizer. Fix OneFoldFitMerge that was given empty list as input.

[contrasting] implement bootstrap confidence interval both for pointwise stationary models and for elevation-temporal models. accelerate bootstraping with multiprocessing & storing of fitted functions only (storing the estimator was impossible).

[contrasting] add histogram for model repartition & evolution of trends. improve preliminary_analysis.py