-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

Some tests that used to mock the cache internals of ConfigurationModels
had to be modified to use CacheIsolationTestCase instead (the things
they were mocking no longer exist).

Fix constraints to not have a lingering pin on edx-when. And
add constraint on version of mock that supports python 3.5.

And then a general make upgrade.

* Bumping edx-enterprise version

* Running make upgrade to bump edx-enterprise

* contraining a package

* fix

* adding yet another constraint

Updating the django-rate-limit requirement.
updated the django-ratelimit to use unreleased version that supports Django 2.2

* Constraining edx-rest-api-client

* Decreased pin on edx-rest-api-client from <3.0.0 to <2.0.0

Unpin several more outdated dependencies whose changelogs don't contain any significant backwards incompatible changes. Also add "moto" to the list of packages to uninstall from existing environments, since it requires a jsondiff version that clashes with the one we now use (triggering a harmless but distracting warning on dependency updates).

We can potentially stop using path.py/path altogether by switching to pathlib in the Python 3 standard library, but that merits a separate PR of its own.

Also, note that I'm not actually unpinning freezegun; different PRs restricted it in both constraints.txt and test.in, I'm just removing the latter redundant constraint.

Added the link to latest master commit of GitHub for Django 2.2 support.

Removing the moto.

django-appconf bump version using commit hash for django2.2

This is step 3 of DE-1824.

Also update:
* six 1.13.0 => 1.14.0
* edx-django-utils 2.0.2 => 2.0.3
* skip test that checks all model changes have migrations.  (We defer
  this to step 4.)

Removed the version constraint for django-mysql
Also pinned the freezegun version to 0.3.12 as the latest version is causing failures.

Bump django-filter.
Rename the name to field-name.