Make bespoke query for permissions-for-roles.

This is mostly an experiment to see if SQLAlchemy Core works better than the
ORM for this use case.
Migrate entirely to SQLAlchemy Core.

The Core-based code will need a lot of cleanup and refactoring.
Factor out null_to_empty_string.
Add copyright notice to database.py.
Move common output patterns to output.py.

This makes the endpoints for permtools extremely small!
Remove dead ORM code.
Add ability to check roles of people.

This necessitated some more table definitions.

I also changed the definition of roles_for_people() to allow roles to be
specified by human-readable name, since some roles don't have aliases.