Add option to override owner

[nnutter]

We could support specifying an owner when creating a database from a template other than template1 that would reassign ownership of existing objects to that owner. This also implies that --owner and --based-on do not need to be mutually exclusive.

The owner of a database can be looked up with:

SELECT rolname FROM pg_database JOIN pg_authid ON pg_database.datdba = pg_authid.oid WHERE pg_database.datname = 'template1';

The owner can be reassigned with:

REASSIGN OWNED BY postgres TO genome;

[nnutter]

#31 addresses most of this but does not address reassigning ownership of all objects, only the database.