More unified preload file changes
Start conversion of kernel classes to namespaces

- XoopsObject, XoopsObjectHandler and XoopsPersistableObjectHandler split into separate files
- XoopsModel classes converted into namespaces
- Fixes for some legacy compatibility issues introduced with earlier Doctrine conversions
- Criteria classes split into separate files
- Dtypes converted into namespaces
- remaining classes in htdocs/kernel adapted to changes in above
A few module updates for recent namespace changes

Includes some Doctrine conversions, too.