-Upgrade edx-drf-extensions
-settings-update

Remove DOP apps from INSTALLED_APPS.
Remove DOP libraries from requirements.

Remove duplicate constraints in requirements/constraints.txt uncovered by the recent change in pip-compile output format. I sorted the pinned dependencies by name to try and make it more obvious if this happens again. I also upgraded to pip-tools 4.5.1, which removes the line numbers from the enhanced pip-compile output added in 4.5.0, which should reduce future diff churn and merge conflicts but means that there's a large diff this one last time.

Also unpin edx-search again after the previous change to do that was apparently broken by a merge conflict.

- Reimplement `djcelery.common.respect_language` utility function so we
  can drop the dependency.
- Loosen `celery` pinning to a range, which brings in a fix for a
  possible crash bug

Also, pin `path` to 13.1.0 for now in order to continue supporting py35.

* Bumping edx-enterprise version

* Running make upgrade to bump edx-enterprise

* contraining a package

* fix

* adding yet another constraint

Django-auth-toolkit update

Pinned the latest commit from github to get Django2.2 support in testing.
Pinned the zipp<2.0.0 to get Python<3.5 support too.

Django 1.11 Changelog - https://docs.djangoproject.com/en/2.0/releases/1.11.14/

This reverts commit a7fa0c21.