further work on contributor page and sitemap

- create a new Contributor model, which is just a proxy class for User
- finalize first version of the contributor page
- add contributors to sitemap
- bonus: improve sitemaps to generate only url and lastmod attributes
  (the only ones used by search engines) and use last validated contribution
  for lastmod
3 jobs for contributor-page in 10 minutes and 8 seconds (queued for 12 seconds)
Name Stage Failure
test-style Test
Installing collected packages: pyflakes, pycodestyle, mccabe, flake8
WARNING: Running pip as the 'root' user can result in broken permissions and conflicting behaviour with the system package manager. It is recommended to use a virtual environment instead: https://pip.pypa.io/warnings/venv
Successfully installed flake8-4.0.1 mccabe-0.6.1 pycodestyle-2.8.0 pyflakes-2.4.0
WARNING: You are using pip version 21.2.4; however, version 21.3.1 is available.
You should consider upgrading via the '/usr/local/bin/python -m pip install --upgrade pip' command.
$ flake8 --config=.flake8
./ippidb/ws.py:8:1: F401 'django.views.generic.detail' imported but unused
Cleaning up file based variables
ERROR: Job failed: command terminated with exit code 1