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/scripts/run-liccheck.sh

@@ -0,0 +1,15 @@
+#!/bin/bash
+
+# Script to run liccheck using poetry, because we use poetry but liccheck uses
+# requirements.txt.
+
+# http://redsymbol.net/articles/unofficial-bash-strict-mode/
+set -euo pipefail
+
+if ! command -v which; then
+	echo "You must have poetry installed to run this script."
+fi
+
+poetry export --without-hashes --output requirements.txt
+liccheck
+rm -f requirements.txt