Materialized Views in SQLAlchemy

[bencap]

As we add more to the project, it is becoming more useful to have materialized views which can provide quicker access to some common and/or important queries. This is particularly useful for #375 and #89 right now, but will also probably be useful in other contexts later on.

We should at minimum:

• Be able to define a materialized view in SQLAlchemy
• Use the view as we would any other model
• Migrate the view with Alembic