[projection snowfall] add preliminary analysis for the work on model with effect related to the GCM or RCM type.

[projection snowfall] improve one_fold_fit_merge.py. improve interval for the sensitivity plot. Add is_temperature_interval and is_shift_interval to define the intervals.

[refactor] fix issue. the temporal covariate is the the anomaly of temperature smoothed with a spline

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