Merge branch 'dbtests' into merge

- Add more tests.
- Add a TODO about maintainer column in table override.
- Convert class Override to ORMObject.
- Improve class Suite.
- Fix and improve class Component.
- Convert class Priority to ORMObject.
- Convert class Section to ORMObject.
- Convert class OverrideType to ORMObject.
- Clean up some old, now obsolete comments.

Signed-off-by: Torsten Werner <twerner@debian.org>