Move db.sql.util to db.util

Now that sqlalchemy is providing the database abstractions, there is no
need to hide everything in db.sql. sub-modules. It complicates the code
and provides a futher layer of indirection.

Move the db.sql.util.py to db.util.py and adapt the importers.

mediagoblin/plugins/oauth/migrations.py

@@ -19,7 +19,7 @@ from sqlalchemy import (MetaData, Table, Column,
                         Integer, Unicode, Enum, DateTime, ForeignKey)
 from sqlalchemy.ext.declarative import declarative_base
 
-from mediagoblin.db.sql.util import RegisterMigration
+from mediagoblin.db.util import RegisterMigration
 from mediagoblin.db.sql.models import User