SQLAlchemy 2.0 Support

[kadler]

Quite a few changes are needed, though I have some preliminary code working. I was mostly focused on SQLAlchemy 1.4 support for 0.9.3.

The biggest issue is that we use the SQLAlchemy query interface to implement metadata queries. SQLAlchemy 1.4 still supports the SQLAlchemy 1.3 style interface by specifying a list of columns, but SQLAlchemy 2.0 no longer supports this. I'm not sure how difficult it would be to support both 1.3 and 2.0, though we may be able to make a wrapper for 1.3 to implement the 1.4+ behavior for select.

There are a few other things here and there that need to be changed as well as new features to be implemented.