in case the avatar is not changed by the user we must resend the still valid hash.
if we do not save the hash here, gajim advertises an empty photo element after publishing the vCard,
which removes the avatar for all receiving clients of the photo element update
- Add support for Pubsub Avatars
- Dont poll for vCard Updates, only use XEP-0153
- Dont cache vCards
- Store the avatar SHA of roster contacts in the DB
- Store the current SHA of each contact in the Contacts Object
- Move some code into the ConnectionVcard Class
