Draft: Noissue - Port scripts to python3

This is a test MR to backup https://jira.eyeo.com/browse/DEVOPS-1042

• Ports all python scripts to python3 by running 2to3
• Uses markupsafe.Markup instead of jinja2.utils.Markup. More info: https://stackoverflow.com/a/71645733/4617744

Pending issues:

• 2to3 auto generated some xxx_todo_changeme variables. Those names should be properly updated.
• tox.ini was also updated to run with python3. Unfortunately, running tox throws the following error:

$ tox
...
py37 run-test: commands[2] | python ensure_dependencies.py
Traceback (most recent call last):
  File "ensure_dependencies.py", line 380, in <module>
    resolve_deps(repo)
  File "ensure_dependencies.py", line 317, in resolve_deps
    source, rev = merge_seqs(sources.get('*'), sources.get(vcs))
ValueError: not enough values to unpack (expected 2, got 0)
ERROR: InvocationError for command /builds/eyeo/devops/legacy/sitescripts/.tox/py37/bin/python ensure_dependencies.py (exited with code 1)
___________________________________ summary ____________________________________
ERROR:   py37: commands failed