Separate registered and autoregistered QObjects

Currently, a new client gets a list of _all_ registered QObjects,
whether they were explicitly registered or not.

This leaks internal information which the clients cannot use right away
anyway.

Change-Id: I4b25a731e9bc2d646f903057b409aecd34dc7f11
Reviewed-by: Milian Wolff <milian.wolff@kdab.com>