Upgrade dependencies

[trygvis]

The dependencies really needs a bump, but both SQLAlchemy and Flask have breaking changes from new major versions. This needs to be reviews/fully tested, but there are also some stale libraries that we depend on.

Misc related issues:

• kvesteri/sqlalchemy-continuum#255
• Flask-SQLAlchemy seems to only support Flask v1 in their 3.0 version, but that has not been released yet. However, I couldn't find any particular reason why Flask-SQLAlchemy wouldn't work from the changelog.
• flask-bower seems stale and doesn't work because flask._compat is gone. Seems easy to fix the module itself, but it probably needs a fork+fix or maybe we can just rewrite something custom.

[trygvis]

It would be nice to drop the recent workarounds for missing auto-detection of http vs https when using flask.url_for() with this: https://werkzeug.palletsprojects.com/en/2.0.x/middleware/proxy_fix/