* Updating Python Requirements

* Don't rely on pip-compile cache

* Fix tornado dependency resolution

Bumping edx-organizations will add history to the Organization model.

DE-1510

This also pins scipy to version <=1.2.1 in constraints.txt, as 1.3.0 requires py3.5 or above

was causing issues with PT exam configuration dashboard launch

Extra constraints needed to be added for pytest-randomly and tornado,
both of which have dropped Python 2 support.

Running make upgrade to bump edx-entprise from 1.2.3 to 1.2.5. Also, updating constraints.txt to prevent a backwards incompatible update from oauthlib

Bumped version of django-simple-history

Bumping django-simple-history in other requirements files

Removing the django-simple-history constraint as it is no longer an issue

Removing the comment from requirements/constraints about django-simple-history