Delete non security classes in correct order in database import

Hello,

I fixed the removal of non security classes during database import (merge=false).
The old algorithm does not sort the classes by inheritance correctly.
Additionally, I fixed some issues with key strings not converted to lower case.
Maybe it would make sense to use a case insensitive HashMap which converts the keys to lower case before every get, put, containsKey and remove. Would be less error prone.
Both test suites were fine.

Regards,

Olaf