Automatic formatting via black + CI support

[volkm]

• Use black for automatic Python code formatting. After installing the black package, code can be formatted using black .
• CI support for checking and applying code formatting, similar to the Storm and pycarl workflows.

[sjunges]

Great. Does this format .rst, .ipynb and .py files?

[volkm]

Now it formats .py and .ipynb files ;)
.rst files are not formatted but they should also not contain any Python code anymore, because the documentation is in the notebooks.

[volkm]

@sjunges can I merge it?

[volkm]

Merging after positive feedback by Sebastian.