ENH: Pre commit

[hongyeehh]

Adding pre-commit function to the repo.
Corrected some flake8 errors, therefore a lot of file changes :).

Two functionalities:

• Enabling pre-commit on your own computer: link
• This also contains a CI that triggers pre-commit every time a PR and change in file occurs (if it works :)): link

Update: The CI works (see below for commits)! We do not need to worry about black and flake8 formatting anymore :)

closes #458. Additionally suppresses the warnings for PostGIS tests

[codecov]

Codecov Report

Base: 98.18% // Head: 98.18% // No change to project coverage 👍

Coverage data is based on head (949d3b5) compared to base (ebc11aa).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #459   +/-   ##
=======================================
  Coverage   98.18%   98.18%           
=======================================
  Files          39       39           
  Lines        1877     1877           
  Branches      324      324           
=======================================
  Hits         1843     1843           
  Misses         13       13           
  Partials       21       21           

Impacted Files	Coverage Δ
trackintel/geogr/distances.py	94.56% <ø> (ø)
trackintel/io/dataset_reader.py	100.00% <ø> (ø)
trackintel/io/file.py	98.00% <ø> (ø)
trackintel/io/postgis.py	95.60% <ø> (ø)
trackintel/preprocessing/filter.py	100.00% <ø> (ø)
trackintel/preprocessing/positionfixes.py	98.78% <ø> (ø)
trackintel/analysis/tracking_quality.py	100.00% <100.00%> (ø)
trackintel/preprocessing/triplegs.py	100.00% <100.00%> (ø)

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[hongyeehh]

I am merging this to resolve our tests errors and continue working on the conda deployment :)

This PR affects no functions but only includes code format changes.