This adds a method that returns only a contact if there is an exact match,
instead of a contact where only the barejid matches.
We need this when we update the Caps of a contact.
- 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