-Updated middleware setting to use use middleware insted of
middleware_classes
-github install of django-method-override fork to support
new style middleware in django1.11

This will remove imports from __future__ that are no longer needed.

https://docs.python.org/3.5/library/2to3.html#2to3fixer-future

Implementation details:
* Anonymous users are assigned a unique ID (like 
  `anon42c08f9996194e2a9339`) which gets stored in the django session.
  `block.scope_ids.user_id` and `block.runtime.anonymous_student_id`
  will both return this value.
* User state for anonymous users is stored in the django cache and
  automatically expires as the cache gets pruned. Because user state is
  stored, anonymous users can use interactive blocks like capa problems.
* There is no mechanism for upgrading to a registered account and
  keeping user state since the user state store for anonymous users
  (EphemeralKeyValueStore) is completely different than the one for
  registered users (DjangoKeyValueStore/"CSM"), and has no "list all
  keys" functionality.
* "User State Summary" field values are shared among [recently active]
  anonymous users but are not shared with registered users.
* Anonymous users can only access the `public_view` of XBlocks, not the
  regular `student_view`.

- retires toggle DISABLE_DEPRECATED_LOGIN_POST
- permanently removes /login_post

Now that studio signin has been retired, we are able to remove the
unused /login_post endpoint.

ARCH-1253

This completes the work started in https://github.com/edx/edx-platform/pull/19453
to use the LMS login and registration for Studio, rather than Studio
providing its own implementation.

LMS login/registration are being used for the following reasons:
1. LMS logistration properly handles all SSO integrations.
2. A single logistration is simpler to maintain and understand.
3. Allows Studio to work more like all other IDAs that use LMS
logistration.

The original switch to use LMS logistration for Studio also added the
toggle `DISABLE_STUDIO_SSO_OVER_LMS` to provide the community some
additional time for switching. This commit removes this toggle, which
at this point means all deployments will use the LMS logistration.

This change requires sharing cookies across LMS and Studio. Should that
prove to be a problem for certain Open edX instances, there are
discussions of possible alternative solutions.
See https://github.com/edx/edx-platform/pull/19845#issuecomment-55915425...

Required these be added to CMS since enterprise is installed in the CMS
and there are import failures when these keys don't exist

We need to do this because when I tride to go to the JSON serializer a
bunch of tests started failing because various parts of our code are
putting things into the session that are not JSON serializable.

We can't keep using the default pickle serializer because it defaluts to
using the highest available protocol and that will cause issues with the
python 2 to 3 upgrade since both will be running in production at the
same time.  We need to use a version of the pickle protocol that both
can use interchangably.

We also need to make sure we read with latin1 encoding to make datetimes
work correctly between the two versions of python.

This will force a logout as sessions fail to load but this should be a
more performant and secure serializer moving forward.  The reason we
overwrote it in our config is that it previously used to be the default
and we didn't want things to breake and force logouts when we changed
it.  We're no more okay with people getting logged out.

If this isn't installed, the sample_task provided by
openedx.core.djangoapps.heartbeat isn't imported, and thus are never
registered with the celery workers.  This sample_task is used for the
extended heartbeat api call. Since the celery heartbeat check is turned
on by default, we should also make sure this djangoapp and thus
sample_task is registered by default. Otherwise the extended heartbeat
check fails with the default configuration.

* Always run CSMHE migrations for every application in all contexts

API docs are now always available, no more toggle to enable them.

[ENT-2191]

ENABLE_MKTG_SITE has been serving double duty to both indicate that
an Open edX installation is using a Drupal marketing site AND
is using the Publisher workflow tool for managing course metadata.

But now that publisher-frontend is available and the Publisher
feature is no longer tied to the marketing site, we want to tease
apart those two concerns. Hence ENABLE_PUBLISHER.

Only really used so far in Studio, to control which fields are
shown (if using Publisher, some fields are only editable in
Publisher).

https://github.com/edx/edx-platform/pull/20645

This introduces:
* A new XBlock runtime that can read and write XBlocks that are persisted using
  Blockstore instead of Modulestore. The new runtime is currently isolated so
  that it can be tested without risk to the current courseware/runtime.
* Content Libraries v2, which store XBlocks in Blockstore not modulestore
* An API Client for Blockstore
* "Learning Context" plugin API. A learning context is a more abstract concept
  than a course; it's a collection of XBlocks that serves some learning purpose.

* Update Financial Assistance logic

Use the zendesk proxy app instead of the unsupported zendesk library.

* Move to pre-fetching the group IDs.

Rather than making extra requests to zendesk to list all groups and find
a specific group ID. Just make a pre-filled list of group IDs for the
groups we care about.  When a group name is passed in, it is checked
against this list and the ticket is created in the correct group so the
right people can respond to it.

openedx.core.djangoapps.ccxcon.tasks.update_ccxcon is not get auto
discovered by celery. Adding it to CELERY_IMPORTS to be explicitly
added.

PROD-283

Fix Unregistered Task

openedx.core.djangoapps.bookmarks.tasks.update_xblock_cache task is not
getting autodiscovered by celery and needs to be imported explicitly

PROD-284

This reverts commit 5e8f90ca.