Added a foreign key relationship to the create table statements.

- MySQL will also use the InnoDB engine now.
- Added a ping call in the MySQL Cursor cache mechanism
- Added a rollback call when a MySQLError occurs
- Removed 'delete_orphans' which is not needed anymore due to foreign key constraints and delete on cascade
- Changed SQLDatabase to accept options to create a cursor factory, instead of taking a pre-created cursor factory
Changed default cursor type for mysql from DictCursor to Cursor.