Mv db.sql.base to db.base

This concludes the db.sql.* -> db.* move. Our db abstraction layer is
sqlalchemy, so there is no need to a separate db.sql.* hierarchy.

All tests have been run for each of the commit series to make sure
everything works at every step.

mediagoblin/plugins/oauth/models.py

@@ -19,7 +19,7 @@ import bcrypt
 
 from datetime import datetime, timedelta
 
-from mediagoblin.db.sql.base import Base
+from mediagoblin.db.base import Base
 from mediagoblin.db.models import User
 
 from sqlalchemy import (