[1.5.x] Fixed #19573 -- Allow override of username field label in AuthenticationForm

Backport of cdad0b28d from master.
[1.5.x] Fixed #19588 - Added create_superuser to UserManager docs.

Thanks minddust for the report.

Backport of 4da5947a87 from master
[1.5.x] Fixed #10239 - Added docs for modelform_factory

Thanks ingenieroariel for the suggestion and slurms for the review.

Backport of 71d76ec011 from master
[1.5.x] Fixed #19437 - Clarified pip install instructions in contributing tutorial.

Backport of 9f9a7f03d7 from master
[1.5.x] Fixed #19585 -- Fixed loading cookie value as a dict

This regression was introduced by the 'unicode_literals' patch.
Backport of f08e739bc2 from master.
[1.5.x] Fixed #19488 -- Made i18n_patterns redirect work with non-slash-ending paths

Thanks Daniel Gerzo for the report and the initial patch.
Backport of bcdb4898c from master.
[1.5.x] Fixed #18026 -- Don't return an anonymous dict if extra_data in storage is empty.

Backport of 97121cb9 from master.
[1.5.x] Fixed #19024 -- Corrected form wizard docs for get_form_prefix.

Backport of 17f8496fe from master.
[1.5.x] Fixed typo in file storage docs.

Thanks Jørgen Abrahamsen.

Backport of 0ca2d1e.
[1.5.X] Added details on minified jQuery and DEBUG mode for contrib.admin.

Thanks Daniele Procida.

Backport of 4720117a31 from master
[1.5.x] Fixed code examples in which render() calls were missing `request` parameter.

5362134090adce86c755a6ab48831ba834b70704 from master.
[1.5.x] Minor DEBUG setting reference formatting edit.

1bbd36a36add9b15db43014cf5e7bdb72a86fef1 from master.
[1.5.x] Fixed #19092 -- Completed Lithuanian date/time formats

Thanks Tadas Dailyda for the report and the patch.
Backport of 2f8ab2f1b0 from master.
[1.5.x] Fixed #19605 - Removed unused url imports from doc examples.

Thanks sergzach for the suggestion.

Backport of 43f89e0ad6 from master
[1.5.x] Clarified WizardView.get_form_prefix doc, refs #19024

Backport of c9b577ead6 from master
[1.5.x] Fixed #19614 -- Missing request argument in render call.

Thanks Dima Pravdin for the report.

Backport of 74d72e2.
[1.5.x] Fixed a typo in the error reporting docs.

Backport of 83d0cc52.
Updated core translations
Updated localflavor translations
Updated contrib apps translations