Smaller logging improvements

[heikoklein]

This PR converts print-statements to logger-statements and addresses #1016 .
It also makes logging of metadatastandards-deviations rather a info than a warnings. The aerocom had 3 metadatastandards while pyaerocom tests for a 4th and newer metadatastandard which isn't really needed yet.

closes #1016

[codecov]

Codecov Report

Attention: Patch coverage is 85.71429% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 79.84%. Comparing base (8c7a57f) to head (5bbece4).

❗ Current head 5bbece4 differs from pull request most recent head 7792ed3. Consider uploading reports for the commit 7792ed3 to get more accurate results

Files	Patch %	Lines
pyaerocom/_logging.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##           main-dev    #1018   +/-   ##
=========================================
  Coverage     79.84%   79.84%           
=========================================
  Files           108      108           
  Lines         18845    18845           
=========================================
+ Hits          15046    15047    +1     
+ Misses         3799     3798    -1     

Flag	Coverage Δ
unittests	79.84% <85.71%> (+<0.01%)	⬆️

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