This reverts commit 1f32bc63.

* Renamed OAuth2Authentication to BearerAuthentication
* Added back OAuth2Authentication name
-there are libraries such as edx-enterprise that still import OAuth2Authentication.  The OAuth2Authentication class should be fully removed when everything is importing BearerAuthentication correctly

Upgrade django-toolbar.

https://openedx.atlassian.net/browse/BOM-1036

* Updating Python Requirements

* Constrain edx-when version for now

-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Unpin several more outdated dependencies whose changelogs don't contain any significant backwards incompatible changes.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.