[1.7.x] Fixed #22300 -- Fixed crash in migrations when changing non-relational field to relational.

Backport of 35ed792cf2 from master
[1.7.x] Fixed #22087 -- Made AdminReadonlyField respect ModelForm Meta overrides.

Backport of 16afffffe8 from master
[1.7.x] Fixed #22315 -- str/bytes mismatch in staticfiles

Previously, `ManifestFilesMixin.read_manifest` failed in Python 3
because `json.loads` accepts `str` not `bytes`.

Backport of 86dcac4634 from master
[1.7.x] Fixed #22331 -- Fixed migrations ProjectState to ignore unmanaged models.

Backport of 69d4b1c3ea from master
Revert "[1.7.x] Fixed #22331 -- Fixed migrations ProjectState to ignore unmanaged models."

This reverts commit bf69375c4d2eaec4f00c646b9e7e84a9397d1a20.
[1.7.x] Fixed #22322 -- Fixed incorrect explanation of what managed=False does.

refs #14305.

Thanks Adrian Klaver for the report.

Backport of 9b7ba8af1b from master
[1.7.x] Fixed #12030 -- Validate integer field range at the model level.

Thanks to @timgraham for the review.

Backport of 1506c71a95 from master
[1.7.x] Fixed field deconstruction tests failures introduced by 1506c71a95.

refs #12030.

Backport of ff874f363c from master
[1.7.x] Add some syncdb deprecation stuff into the deprecation doc

Backport of 378359de1c from master
[1.7.x] 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.

Backport of 42336c84a0daedfd8242333622eefe202e32398e from master