Fixed #23061: Avoided setting a limit on a query for get with select_for_update on Oracle

Thanks Michael Miller for reporting the issue.
Stop errors on older Spatialite versions that miss some tables
Updated links for continous integration server.
Removed code that assumed BooleanField could be null.

Such a field will no longer pass model validation.
Fixed broken links in docs.
Fixed #21792 -- Documented Form.has_changed()

Thanks bjb at credil.org for the suggestion and
Ivan Mesic for the draft patch.
Fixed #21603 -- Fixed complex RawQuerySets queries on some versions of SQLite.
Fixed #23244: Error altering FK to non-FK in migrations
Moved index dropping after FK dropping to please MySQL and fix test
Fixed #23226: Model options appearing as bytes type in migrations
Removed a doc reference to the deprecated `mimetype` kwarg.
Fixed #23252: Call out removed features in release notes.

Also added StrAndUnicode mixin note to deprecation plan as it was
missing.
Added a missing unicode_literals that caused a test failure after refs #23226.
Use smart_text rather than naive forcing-to-unicode for state reading
Fixed flake8 warning.
Fixed #22982 -- Added GenericRelatedObjectManager.__str__. to prevent crash.

Thanks bendavis78 for the report.

Forwardport of 29585e9b6a from stable/1.7.x
Don't treat .pyc/pyo files as migrations. Refs #23237 among others.
Fixed #23257 -- Updated docs for new django-jython release.
Removed some tabs in the docs.
Fixed #23099 -- Removed usage of deprecated initial data in Django's test suite.

Thanks Claude Paroz for assistance with debugging the tests.