Instead of saving the vcard data on the contact model itself

VCards will now always be used.

and not via the chatbox view (fixes some failing tests also).

- Refer to VCards instead of Avatars where appropriate
- Fetch VCards for non-groupchat messages as well

Entity items weren't being fetched from cache.

Apparently this bug only surfaced because with Ejabberd the upload
service is nested one level deeper than with Prosody.

we don't yet have a connection then, so listen to
`connectionInitialized` instead.

so that `hidden` class gets applied to the right element

- Filter did the opposite of what it was supposed to do
- Wrong bind context
- Should actually be mam:2, issue was server misconfiguration

if the fullname is not available.

This allows us to cache them for longer.

- set `username` on the message object,
  instead of always using `fullname` with fallback to `jid`.
- Distinguish better between `groupchat` messages and normal
  messages in `getMessageAttributesFromStanza`