Update fix of normalize_D in the case of wo weights. Add density plot in compute results for all stages and add some plots in results.

Add Paolo's first implementation of this paper: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2822360/

- Add new results for stage4.

- Add stage4 (results and experiments);
- Do not save model object.

- Add diamonds in experiment scripts and add factorize run_compute_results.sh script;
- Add best params for diamonds dataset.

- Remove extracted_forest_sizes_number parameter from compute_results.py and retreive the value instead;
- Add almost all remaining experiment config files of stages 1, 2 and 3;
- Add almost all remaining result plots of stages 1, 2 and 3;
- Add some temporary scripts to run all stages experiments.

- Add command lines example for stage 3;
- Add experiment_id option that is useful sometimes;
- Fix subsets_used param;
- Remove experiment_id in config experiment file names;
- Add config experiment files for stages 2 and 3;
- Add results for stages 2 and 3 (california_housing).