PEP-8 cleanup

Refs #21169
Fixed typo in release notes.
Merge pull request #2000 from loic/docs

Fixed typo in release notes.
Added a warning regarding risks in serving user uploaded media.

Thanks Preston Holmes for the draft text.
A handle of flake8 fixes
Fixed #21515 -- Corrected example of template.Context in documentation.

Thanks to trac user oubiga for the report.
Fixed #21517 -- Added unit test for non-autoincrement primary key with value 0.
Fixed E125 pep8 warnings
All the E125 errors hvae been eradicated.
Fixed #21496 -- Fixed crash when GeometryField uses TextInput

Thanks Rhett Garber for the report and initial patch.
Use 'update_fields' in RelatedManager.clear() when bulk=False.

Thanks Simon Charette for the suggestion.

Refs #21169.
Merge pull request #2005 from loic/ticket21169

Use 'update_fields' in RelatedManager.clear() when bulk=False.
Fixed a deprecation warning introduced by 96dd48c83f.
Fixed #21380 -- Added a way to set different permission for static directories.

Previously when collecting static files, the directories would receive permissions
from the global umask. Now the default permission comes from FILE_UPLOAD_DIRECTORY_PERMISSIONS
and there's an option to specify the permissions by subclassing any of the
static files storage classes and setting the directory_permissions_mode parameter.
Fixed #20867 -- Added the Form.add_error() method.

Refs #20199 #16986.

Thanks @akaariai, @bmispelon, @mjtamlyn, @timgraham for the reviews.
Removed Form._errors from the docs in favor of the add_error API.
Fixed an unescisarily gendered pronoun in a docstring
Enabled makemessages to support several translation directories

Thanks Rémy Hubscher, Ramiro Morales, Unai Zalakain and
Tim Graham for the reviews.
Also fixes #16084.
Closed file after reading pot file

Faulty line was introduced in 50a8ab7cd1.
Fixed comment typos.