Openedx-completion-aggregator

~~~~~~~~~~~~~~~~~~~~

* Transform `openedx.completion_aggregator.progress.*` tracking log events into xAPI using edx-event-routing-backends so
they can be included in Aspects analytics data.

~~~~~~~~~~~~~~~~~~~~

* Emit `openedx.completion_aggregator.progress.*` tracking log events for the
various block/course types

~~~~~~~~~~~~~~~~~~~~

* Replace `xblockutils.*` imports with `xblock.utils.*`. The old imports are
used as a fallback for compatibility with older releases.
* Remove `xblockutils` dependency.

~~~~~~~~~~~~~~~~~~~~

* Update GitHub workflows.
* Update requirements to logically organize them and allow scheduled
requirements updates.
* Add base requirements to `setup.py`.

~~~~~~~~~~~~~~~~~~~~

* Add `COMPLETION_AGGREGATOR_AGGREGATE_UNRELEASED_BLOCKS` setting, which
enables the use of course blocks with a release date set to a future date in
the course completion calculation.

~~~~~~~~~~~~~~~~~~~~

* Add Maple support.
* Drop support for Python 2.
* Drop support for Django 2.X.
* Replace Travis CI with GitHub Actions.
* Fix docs quality checks.
* Fix pylint quality checks.
* Fix the build & release pipeline.