thanks to Neven for discovering

updated the test file for density v11

I would normally expect for density file v11,
but I have earlier corrected it.
Now it was not working with our example file so I
corrected back.

fix trailing whitespace and end of line

- more consistent module names
- removing a duplicate
- fixing new flake8 warnings

replaced several string.format with f-strings

updated tracewin_errorstudy to python3
corrected errors from black/flake8

fix minor issue in DTL_CEL class

some minor cleaning as well

Supporting python 3.8 as well
adding missing field maps for tests
version checker added
version checker needs all deps installed

updated style
fix in lib_tw, was catching the wrong type of error
adding some tests for lib_tw

correcting the amount of data per step in v11 Density_PAR?