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
Remove abandoned contacts
Wait for import to be done before writing contacts
Reset importDone at the beginning of sync
Merge pull request #661 from mar-v-in/improve-contacts

Improve contact sync