Small code clean up

[jdebacker]

This PR makes some small changes to the code to make the output of OG-Core cleaner and more readable.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.44%. Comparing base (fdc00e2) to head (ae3983c).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #917      +/-   ##
==========================================
- Coverage   73.46%   73.44%   -0.02%     
==========================================
  Files          19       19              
  Lines        4613     4610       -3     
==========================================
- Hits         3389     3386       -3     
  Misses       1224     1224              

Flag	Coverage Δ
unittests	73.44% <100.00%> (-0.02%)	⬇️

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Files	Coverage Δ
ogcore/demographics.py	71.56% <100.00%> (ø)
ogcore/parameter_plots.py	82.41% <100.00%> (ø)
ogcore/utils.py	88.39% <ø> (-0.09%)	⬇️