[1.7.x] Fixed imports in `Sitemap for static views` example

Backport of 344f37718b from master
[1.7.x] Added missing periods in docs/ref/checks.txt.

Backport of 5d04433903 from master
[1.7.x] Fixed typo in docs/topics/checks.txt.

Backport of 0f90f741de from master
[1.7.x] cater for running tests from another directory than tests - applying existing pattern to newly added test_testcase_ordering as well

Backport of d11e836203 from master
[1.7.x] Fixed #22534: Reinforce swappable documentation
[1.7.x] Fixed #22411: Throw a more helpful error if contenttypes doesn't exist.

Conflicts:
	django/contrib/contenttypes/models.py
[1.7.x] Fixed #23414 -- Updated version numbers in release process doc.

Thanks jaap3 for the report.

Backport of 5c5011ce68 from master
[1.7.x] Update docs to be more clear about nested classes (refs #23418)
[1.7.x] switch out recursive dfs for stack based approach, to avoid possibly hitting the recursion limit
[1.7.x] Fix Python 3 incompatability
[1.7.x] Fixed #23427 -- Documented migrate is required before runserver for default projects.

Backport of fb545e5a27 from master
[1.7.x] Fixed #23430 -- simplified gunicorn deployment docs.

Backport of 77b3907d6d from master
[1.7.x] Fixed #22161 -- Documented send() with no recipients won't raise an exception.

Backport of 0f0a5c07f9 from master