Fixed #21478 -- Corrected docs for when Field.db_type() is called.
Use cached_property for request.GET and request.COOKIES
Unified listing of shell commands/code

- use code-block:: bash
- prefix the command with $
Merge pull request #2105 from funkybob/cleanup_get_post

Used @cached_property for request.GET and COOKIES
Swapped app registry and app config API docs.

Thanks David Larlet for the suggestion.

Also fixed some Sphinx warnings and improved ReST markup.
Removed redundant line
Merge pull request #2114 from levigross/master

Removed redundant line
Added 1.6.2 release note for 542198c1d
Fixed #21627 -- Added unicode_literals to changepassword command.

Fixed a crash when executing changepassword command when the user object
representation contained non-ASCII characters.
Added missing newline in previous commit.
Removed a few gratuitous lambdas.
Beefed up the comments for AppConfig.all_models.
Turned apps.ready into a property. Added tests.
Fixed #21206 -- No longer run discovery if the test label doesn't point to a package or directory.

Thanks thepapermen for the report and Carl Meyer for the review.
Added basic tests for get_app_config[s].
Made unset_installed_apps reset the app registry state.

Previously the _apps/models_loaded flags could remain set to False if
set_installed_apps exited with an exception, which is going to happen as
soon as we add tests for invalid values of INSTALLED_APPS.
Made the AppConfig API marginally more consistent.

Eliminated the app_ prefix that was more confusing than useful.
Normalized exceptions raised by AppConfig.create.

It raises ImportError whenever an entry in INSTALLED_APPS points
(directly or indirectly via AppConfig.name) to a non-existing module
and ImproperlyConfigured in all other cases.

Catching ImportError and re-raising ImproperlyConfigured tends to make
circular imports more difficult to diagnose.
Added tests for invalid values of INSTALLED_APPS.
Added file forgotten in previous commit, plus one more test.