Annulation des reventes

Closes #191

See merge request cof-geek/gestioCOF!297

Autre idée pour réparer le hook de pre-commit

See merge request cof-geek/gestioCOF!322

bda.tests -- Silence syncmails in setup

See merge request cof-geek/gestioCOF!320

core -- Add and apply black, flake8, isort to CI and pre-commit

Closes #200

See merge request cof-geek/gestioCOF!317

Script de pre-commit plus robuste

See merge request cof-geek/gestioCOF!319

On CI:
- black and isort in check mode must pass.
- flake8 only prints errors
  WIP: make it also failed.

On pre-commit:
- black and isort will format staged files, if installed on path.
- flake8 prints its output if necessary.

... and use env var for pip install location.

cof -- Add tests for registration views

See merge request cof-geek/gestioCOF!287

core -- Disable coverage in GitLab CI

See merge request cof-geek/gestioCOF!318

kfet.tests -- Add tests for perform_operations view + small things

See merge request cof-geek/gestioCOF!313

core -- Add code coverage to CI

See merge request cof-geek/gestioCOF!314

Delete an error never raised, and avoid duplicate messages.

kfet -- Remove unused view

See merge request cof-geek/gestioCOF!312

Quelques tests pour les vues BdA

See merge request cof-geek/gestioCOF!280