DBSessionMeta no longer convieniently exposed.

[bazylhorsey]

Before in 0.5 our team used:

    def get_db(self) -> DBSessionMeta:
        return self.db

Now in 0.6 we have to use:

    def get_db(self) -> Any:
        return self.db

This is due to recent changes to middleware.py because the method now has internalized classes.