Create match failures as data checks

We should make import errors (group name mismatch, etc.) better handleable for admins.

• Introduce a preference defining which kinds of data are expected to be seeded by Untis (i.e. expected to not generate a match on import, but create a new obejct)
• For all other kinds of data, if an object is newly created, create a data check result wit ha solve option to select another object for the match