Add logging, fix Node and test Femnist

config.ini

main.ipynb

src/decentralizepy/datasets/Data.py

src/decentralizepy/datasets/Dataset.py

src/decentralizepy/datasets/Femnist.py

src/decentralizepy/node/Node.py

src/decentralizepy/training/Training.py

src/decentralizepy/training/__init__.py

src/decentralizepy/utils.py