Fixed #21213 -- Added docs for Django's mailing lists.

Added docs/internals/mailing-lists.txt documenting the use of django's
mailing lists. All references across docs changed to point to this page.

The referencing makes use of substitution because there's no way to make
a :ref: link in a non-inline fashion in Sphinx. It also makes use of
rst_epilog Sphinx conf for making this substitutions across all the
docs.
Fixed #6681 -- Don't break docutils when rendering reStructuredText.

Don't set a global default interpreted role function for reStructuredText.
Instead, use the `default-role` directive to change the default only within
the `parse_rst()` function.

Thanks Malcolm Tredinnick for the report.
Fixed #11277 -- Hid labels of fields with HiddenInput widget in admin forms.

Thanks bartTC for the report.
Fixed #21217 -- Avoid connecting `(pre|post)_init` signals to abstract senders.
Fixed #21189: Cleaned up usage of bare except clauses.

Thanks to berkerpeksag for the report and to claudep
for the review.
Fixed #21150 -- select_related + annotate join promotion failure

Added tests for a .annotate().select_related() join promotion failure.
This happened to work on master but was currently untested.
Improved Query join promotion logic

There were multiple cases where join promotion was a bit too aggressive.
This resulted in using outer joins where not necessary.

Refs #21150.
Fixed #21161 -- Timezone-related tests on Windows.

Thanks Xelnor for the patch.
Simplified a test by using CapturedQueriesContext
Fixed #18414 -- qs.exists() for sliced distinct queries
Fixed #21174 -- transaction control in related manager methods
Improved error message while setting GeometryProxy
Fixed #21235 -- Disabled savepoints for old versions of SQLite.

Thanks Ramiro for the report.
Re-added link to SQLite notes from DB section of install doc.
Fixed #21236 -- Allowed migrations to work with unique_together tuples.

Thanks hjwp for the report.
Fixed #18263 -- Corrrected handling of hidden fields in tabular admin inlines.

Thanks hvdklauw for the report and patch.
Fixed #21241 -- Avoid extraneous JOINs in admin changelist search.
Added a link in admin branding block to admin index.

Refs #13749 and #21220.
Revert "Fixed #21241 -- Avoid extraneous JOINs in admin changelist search."

This reverts commit 698dd82eee1cb83f51d4cd39546461bf76976b5e.

The patch introduced a backward incompatible change.
Added min-width for date and time inputs in admin.

refs #21220.