[1.6.x] Fixed #21560 -- Added missing 'slug' field in example code.

Backport of 744aac6dac from master
[1.6.x] Updated translations from Transifex
[1.6.x] Fixed #21510 -- Readded search reset link in changelist search bar

Thanks moritz.pfeiffer at alp-phone.ch for the report and
Tim Graham for the initial patch.
Backport of c7c647419c from master.
[1.6.x] Fixed #21473 -- Limited language preservation to logout

Current language is no longer saved to session by LocaleMiddleware
on  every response (the behavior introduced in #14825).
Instead language stored in session is reintroduced into new session
after logout.
[1.6.x] Added release note for #21473
[1.6.x] Added release note for #21358
[1.6.x] Added release note for #21443
[1.6.x] Additions and edits to the 1.6.1 release notes.
[1.6.x] Fixed #21594 -- Added note about model formsets deleting objects.

This behavior has been fixed in 65e03a424e. refs #10284.
Bumped version number for 1.6.1.
[1.6.x] Added 1.6.1 release date.
[1.6.x] Post release version bump.
[1.6.x] Removed weird unicode char in some de po files

Refs #21601.
[1.6.x] Added 1.6.2 release notes stub.

Backport of ccd80dc3b6 from master
[1.6.x] Fixed #21580 -- Clarified why render() does not return a TemplateResponse object.

Backport of f685f94c98 from master
[1.6.x] Fixed link text for "Testing in Django" in tutorial 5.

Backport of e1cfc4b96a from master
[1.6.x] Fixed #21614 -- improved docs on configuring email for development.

Backport of d599b590eb from master
[1.6.x] Fixed #21539 -- Added example of modelformset_factory's form argument

Backport of 1fa681ee11 from master
[1.6.x] Added internal link to i18n documentation.

Backport of e904d421d06bb53fbc9f55bd129b0b213d9908c5 from master.
[1.6.x] Fixed typo in docs/ref/models/fields.txt

Backport of dfc95d240d from master.