Fixed #20290 -- Allow override_settings to be nested

Refactored override_settings to store the underlying settings._wrapped
value seen at runtime, not instantiation time.
Fixed #20612 -- Fixed incorrect wording in CBV documentation

Thanks to ndokos for the report.
Fixed #19881 -- Documented that get_next/previous_by_FOO uses default manager.
Fixed #20634 - Corrected doc mistake re: staticfiles finders strategy.

Thanks claudep for the catch and bmispelon for the research.
Fixed 17478 -- Allowed queryset overriding in BaseModelFormSet init

BaseModelFormSet.forms is now a cached property instead of being
populated in the __init__ method. This behaviour also matches an
example in the documentation.
Thanks Thomasz Swiderski for the report and Simon Charette for the
review.
Fixed #18872 -- Added prefix to FormMixin

Thanks @ibustama for the initial patch and dragonsnaker for opening the
report.
Merge pull request #1294 from LuRsT/added_prefix_to_form_mixin

Fixed #18872 -- Added prefix to FormMixin
Fixed #20587 -- Made convert_values handle None values
Merge pull request #1295 from LuRsT/fix_sqlite_convert_values_20587

Fixed #20587 -- Made convert_values handle None values
Added missing `versionadded` for `FormMixin.prefix`.
Fixed #20311 -- Make sure makemessages doesn't create duplicate Plural-Forms .po file headers.

Thanks naktinis for the report and initial patch.
Fixed a very old email address of mine still lingering in the AUTHORS file
Fixed errors and inconsistencies in CBV topic documentation.

The code examples should now work correctly.
The `get_context_data` method in the examples was changed when
necessary to adopt a singular style (get context with super(...),
add the extra keys to the dict then return it).

Thanks to Remco Wendt for the initial report and to Tim Graham
for the review.
Fixed #20524  - Described keywords in triaging contrib doc.
Corrected minor typos in FileUploadHandler.receive_data_chunk docs.
Fixed #20643 -- Fixed implementation of JSONResponseMixin in CBV docs

Thanks to Michal Sládek for the report and initial patch,
and to loic84 for the review.
Fixed #20644 -- Add ModelFormMixin.fields to the CBV flattened index

Thanks to Tim Graham for the report and review.
Clarified get_list_or_404 docs, refs #14150.
Fixed #14881 -- Modified password reset to work with a non-integer UserModel.pk.