moved plotting back from preprocessing to postprocessing to have a single location where all plots are created

Resolve "refac: limit axis in competing skill score plot"

See merge request !286

enhanced multiprocessing switch for debugging

See merge request !285

Resolve "add switch to use multiprocessing"

See merge request !281

update changelog in develop

See merge request !282

default data handler and preprocessing support parameter use_multiprocessing. Parameter is set to False on DEBUG always. /close #297 on pipeline success

Resolve "Transformation parameters in data_handler_single_station must be xarray"

See merge request !277

Resolve "fix separation of scales data handler"

See merge request !272

Resolve "implement lazy data preprocessing"

See merge request !274

data handlers with filters will create negative values, which is incompatible with log transformation. standardization will be used in this cases

Merge branch 'lukas_issue292_feat_data-preprocessing' into 'lukas_issue290_bug_fix-separation-of-scales-data-handler'

include lazy preprocessing

See merge request !275

Merge branch 'lukas_issue290_bug_fix-separation-of-scales-data-handler' into 'lukas_issue292_feat_data-preprocessing'

# Conflicts:
#   mlair/data_handler/data_handler_mixed_sampling.py