Continue contact db sync

- Only add keyrings to contact db that are not expired nor revoked
- Merge all user ids of a key into one contact (#659)
- Update contacts: Changes in keyrings (user id add, user id revoke, change of primary id) will be updated into contact db

TODO:
- delete contact once keyring is removed from OK
- sync: wait for key downloads to complete before changing contact db
Code style