Improve orm XML mapping configuration

[jorrit]

Subject

The *.orm.xml files contained some errors:

• The xsi attributes were not setup properly, preventing validation in an XML editor.
• The default values for three columns were configured using the default attribute. This attribute does not exist. A default value must be configured using the <options> subelement.

I have removed the default values altogether and not replaced them with the right configuration code, because this introduces schema changes. Apparently the bundle works fine without the defaults.

I am targeting this branch, because the changes are backwards compatible.

Changelog

### Fixed
- Fixed validity of *.orm.xml mapping files.

[greg0ire]

Thanks @jorrit !