Fixes plotting, errors and issue #60

- fixes issue #60
- formatting (mostly spacing)
- z-order of data and MC (data always in the front)

Due to formatting changes, here the summary for the first item:
- File https://github.com/kreczko/DailyPythonScripts/blob/be6d218dc2fbbec387f9eb3de8bb7b15f4baf3c0/src/cross_section_measurement/03_calculate_systematics.py lines 214 to 254
- File https://github.com/kreczko/DailyPythonScripts/blob/be6d218dc2fbbec387f9eb3de8bb7b15f4baf3c0/src/cross_section_measurement/04_make_plots_matplotlib.py lines 64 to 89
- rest is format only