Fixed #22315 -- str/bytes mismatch in staticfiles

Previously, `ManifestFilesMixin.read_manifest` failed in Python 3
because `json.loads` accepts `str` not `bytes`.
Fixed #22331 -- Fixed migrations ProjectState to ignore unmanaged models.
Fixed #22322 -- Fixed incorrect explanation of what managed=False does.

refs #14305.

Thanks Adrian Klaver for the report.
Fixed #12030 -- Validate integer field range at the model level.

Thanks to @timgraham for the review.
Add some syncdb deprecation stuff into the deprecation doc
Fixed #22331 -- Made MigrationAutodetector ignore unmanaged models.

This commit reverts 69d4b1c and tackle the issue from a different angle.
Models remain present in the project state, but are now ignored by the
autodetector.
Fixed field deconstruction tests failures introduced by 1506c71a95.

refs #12030.
Fixed #22335 -- Fixed popen_wrapper error on non-English Windows systems.
Merge pull request #2481 from zsiciarz/ticket-22335

Fixed #22335 -- Fixed popen_wrapper error on non-English Windows systems.
Fixed Python 3.4 test failure.
Fixed #22029 -- Removed obsolete advice on registering migrate/syncdb signal handlers.

All signals should now be registered in AppConfig.ready().

Thanks un33k for the report.
Fixed #22341 -- Turned django.db.models.fields.related into a package.