Upgrade Python and dependencies

[davidfischer]

I would like to update the version of Python required for this repository as some dependencies are starting to drop 3.7 (notably Django 4.2 is Python 3.8+). Also, I noticed that the production dockerfile used by fly.io is actually using Python 3.10 so we have a mismatch between dev and production which simply hasn't manifested as an issue because 3.7 and 3.10 are broadly compatible and the site is fairly simple. Standardizing on 3.10 seems fine for now.

The following things need to be updated (outlined here):

• Tox (we should probably just make the command py3 instead of py37.
• Pyproject.toml
• .pre-commit-config.yaml
• .ci.yaml
• README.md
• Remove runtime.txt. This file was used by Heroku but is not used now that we're running on fly.io. Fly uses a dockerfile which specifies the Python version.

[davidfischer]

Just a quick note that I tested this out and there are some issues with some dependencies (notably webob which is used for testing). Some dependencies will need to be updated as well.

[davidfischer]

Fixed by #143