correct data format from join if given as list, prepare host creates separate data directory if hourly data is loaded

add time tracking for some potential bottlenecks, run.py can now run without training AND model_setup, if a model was stored locally

Lukas issue32 refac restructure plot routines in modules

See merge request toar/machinelearningtools!28

# Conflicts:
#	requirements.txt
#	src/run_modules/model_setup.py

added some docs, new plot routine plot_competitive_skill_score, skill score plots are now included in postprocessing, many changes and bugfixes in skill score calculation

bugfix: added start and end to the default kwargs keys, before the time range in all subsets (train, ...) have been equal!

added 4th subset "train_val" that consists on the union of train and val. Is needed for the external skill score calculation. Also added simple MSE function (no need to install sklearn just for mse)

first part of skill score calculation (CASE I and II implemented), added copy of skill_score_plot from felix repository (not checked yet)

minor change in data loading process, there can be now the option to re-download data during preprocessing