* Python code cleanup by the cleanup-python-code Jenkins job.

This pull request was generated by the cleanup-python-code Jenkins job, which ran
```
add_common_constraint; make upgrade
```

The following packages were installed:
`edx-repo-tools`

* Added --django-settings-module to pylint

* Changed position

* Remove django-settings-module from pylint command

* Add django-not-configured in pylintrc

Co-authored-by: Muhammad Soban Javed <58461728+iamsobanjaved@users.noreply.github.com>

* Implement extensions and view support for LTI

* Add missing iss to token

* Add missing requirement, upgrade requirements

* Improving comment

* Add missing exception statement

* Update lti_consumer/lti_1p3/tests/extensions/rest_framework/test_authentication.py

Co-authored-by: Ned Batchelder <ned@nedbatchelder.com>

Co-authored-by: Ned Batchelder <ned@nedbatchelder.com>

This change moves the LTI configuration retrieval to
a Django model that will LTI configuration.
The current model proxies back the to blocks to keep
backwards compatibility.

See reasoning for change at:
https://github.com/edx/xblock-lti-consumer/blob/master/docs/decisions/0001-lti-extensions-plugin.rst

Remove constraints.
Add classifiers.
Update setup.py install_requirements definition.
Update travis file using new requirements.
Create requirements folder.
create pip_tools, base, test and travis requirements files.
Remove old requirement files.
Create Makefile and add upgrade command.
Include requirements files generated using upgrade command.
Update openedx.yml OEPs list.