New forum URLs, drop broken modules, delete OAuth

[HebaruSan]

Problems

On 2023-12-07, Rip Van SpaceDock awoke to discover the world changed around him. Formerly working and supported Python modules no longer loaded:

• Flask-Markdown threw an exception at loading because flask no longer exports Markup
• flask.json no longer exports JSONEncoder
• flask_oauthlib.client had a similar problem that I didn't capture, and all of the OAuth stuff wasn't being used anyway.

This was hacked around by live-editing lib/python3.10/site-packages/flaskext/markdown.py in production 🤮.
From the description, it sounds likely that this broke some part of the site that we don't know about yet.

Motivation

The KSP forum's user profile link format changed (/index.php? was dropped), so recently posted URLs aren't rendered as name-and-link as they are supposed to be.

Changes

• Now the Dockerfile builds for Python 3.10 instead of 3.8, because this is what's current in Ubuntu LTS
• Now we make our own markdown filter from the standard module instead of using Flask-Markdown. As a bonus, the underlying converter is now shared with common.render_markdown (which previously didn't support emojis), so the format will now be reliably consistent.
• Now all the unused OAuth stuff is deleted
• Now we use json.JSONEncoder instead of flask.json.JSONEncoder
• The docker compose file is updated to no longer mount /dev/log because this is OS-specific and was breaking on Windows
• The forum profile parser is updated to support the new format in addition to the old

I'll probably just merge this to keep things moving along...