Remove requirements.txt as a dependency (#1111)

* Remove requirements.txt as a dependency

This converts both docker and tox to use poetry, eliminating usage of
requirements.txt in both flows.

- In tox, uses the tox-poetry package which installs dependencies from
  the lockfile.
- In docker, uses
  https://stackoverflow.com/questions/53835198/integrating-python-poetry-with-docker
  as a reference.

* Don't copy pyproject.toml

* Remove obsoleted docs about requirements.txt

* Add --full-trace option to pytest

* Fix liccheck

liccheck works with requirements.txt, not with poetry, so there needs to
be an extra translation step.

* TEMP: Add WIP fix for pandas issue

This is just to see if the github actions would pass once this fix gets
merged, but it's being reviewed separately.

* Revert "TEMP: Add WIP fix for pandas issue"

This reverts commit 06e38e8cc77f5f3105c6e7a9449901db67aa1c82.

data/data-pipeline/README.md

@@ -279,10 +279,6 @@ After installing the poetry dependencies, you can see a list of commands with th
 For more information, see [nbextensions docs](https://jupyter-contrib-nbextensions.readthedocs.io/en/latest/install.html) and
 see [python-markdown docs](https://github.com/ipython-contrib/jupyter_contrib_nbextensions/tree/master/src/jupyter_contrib_nbextensions/nbextensions/python-markdown).
 
-## Miscellaneous
-
-- To export packages from Poetry to `requirements.txt` run `poetry export --without-hashes > requirements.txt`
-
 ## Testing
 
 ### Background