Ensure continuous support of Django 3.2 and celery v5.0+

[gabor-boros]

Description

This PR ensures that xblock-poll supports

• Python 2.7 - Django 1.11
• Python 3.6 - Django 2.2
• Python 3.6 - Django 3.2
• Python 3.8 - Django 2.2
• Python 3.8 - Django 3.2

Also

• it replaces the CI/CD pipeline with CircleCI
• makes some small adjustments on the README file for better readability
• introduces tox for testing
• adds trove classifiers to setup.py
• bumps package version
• adds missing translations that were committed
• adds support for celery v5.0+

Supporting information

• Related edX GitHub Issue

Celery did remove the celery.decorators module, or at least tasks is not part of that anymore. Therefore, mimicking the previous behaviour, we have to import the current Celery app and use that task. OpenCraft currently upgrading Celery on the edX platform as well, so we wouldn't need to bump xblock-poll twice in the platform:

• https://github.com/edx/configuration/pull/6586
• https://github.com/edx/edx-platform/pull/29046

Dependencies

• N/A

Testing instructions

• Install necessary requirements
• Run tox -- get a coffee, it will take a while because of bok-choy
• Go to the test instance and check this poll and survey to validate it is working even on master
• Export results

Deadline

ASAP

Reviewers

@arbrandes

[pomegranited]

:+1:

• [x] I tested this on the sandbox created for https://github.com/edx/edx-platform/pull/29046 by setting up a course containing the Survey/Poll XBlocks, and ensuring I could download the csv reports. See test course.
• [x] I read through the code
• [x] I checked for accessibility issues N/A
• [x] Includes documentation N/A
• [x] Commit structure follows OEP-0051