Reformat using black and add lint to CI

[fepitre]

The command black -l 80 qubesadmin has been performed together with adding lint job to .gitlab-ci.yml.

[fepitre]

Please see second commit that makes pylint happy. There is minor manual format adjustments.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 73.16422% with 201 lines in your changes are missing coverage. Please review.

Project coverage is 75.06%. Comparing base (0efd8ca) to head (5c07e64).

Files	Patch %	Lines
qubesadmin/backup/restore.py	54.80%	94 Missing :warning:
qubesadmin/backup/core2.py	63.09%	31 Missing :warning:
qubesadmin/app.py	73.63%	29 Missing :warning:
qubesadmin/storage.py	67.21%	20 Missing :warning:
qubesadmin/base.py	86.79%	7 Missing :warning:
qubesadmin/backup/core3.py	85.00%	6 Missing :warning:
qubesadmin/spinner.py	61.53%	5 Missing :warning:
qubesadmin/firewall.py	95.16%	3 Missing :warning:
qubesadmin/devices.py	91.66%	2 Missing :warning:
qubesadmin/events/__init__.py	92.85%	2 Missing :warning:
... and 1 more

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #281   +/-   ##
=======================================
  Coverage   75.06%   75.06%           
=======================================
  Files          51       51           
  Lines        7837     7837           
=======================================
  Hits         5883     5883           
  Misses       1954     1954           

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