Fixed #23914 -- Improved {% now %} to allow storing its result in the context.

Thanks to Tim for the review.
Release notes for ff3d746e8d8e8fbe6de287bd0f4c3a9fa23c18dc
Removed contrib.comments from translations config.
Updated formtools docs to point at new package outside the Django repo.

Refs #23677.
Adjusted a comment to reflect some app refactor changes.
Fixed #23677 -- Removed contrib.formtools
Updated GIS docs to use doc links.
Fixed #23901 -- Documented how to use SpatiaLite with Homebrew.
Fixed #23867 -- removed DateQuerySet hacks

The .dates() queries were implemented by using custom Query, QuerySet,
and Compiler classes. Instead implement them by using expressions and
database converters APIs.
Fixed #23801 -- Added warning when max_length is used with IntegerField
Fixed #23847 -- Improved the email_check example in the auth documentation.
Fixed #23875 -- cleaned up query.get_count()
Fixed #23877 -- aggregation's subquery missed target col

Aggregation over subquery produced syntactically incorrect queries in
some cases as Django didn't ensure that source expressions of the
aggregation were present in the subquery.
Fixed #14664 -- Logged a warning if MiddlewareNotUsed is raised in DEBUG mode.
Fixed typo in docs/topics/forms/modelforms.txt.
Added notes on registering signals in ready() and using dispatch_uid.

Refs #23641.
Fixed cache state dependence for assertNumQueries in test_group_permission_performance.

Refs #20432 and #23746.
Fixed #23641 -- Moved post_migrate signals for contrib apps to AppConfig.ready().
Cleaned up the django.template namespace.

Since this module is going to hold both the implementation of the Django
Template Language and the infrastructure for Multiple Template Engines,
it should be untied from the DTL as much as possible within our
backwards-compatibility policy.

Only public APIs (i.e. APIs mentioned in the documentation) were left.
Imported BaseEngine from the DEP.

i18n is left aside for now.