mod_vcard_muc: Add an alternative method of signaling avatar change When the avatar has been changed, a signal is sent that the room configuration has changed. Clients then do a disco#info query to find the SHA-1 of the new avatar. They can then fetch it as before, or not if they have it cached already. This is meant to be less disruptive than signaling via presence, which caused problems for some clients. If clients transition to the new method, the old one can eventually be removed. The namespace is made up while waiting for standardization. Otherwise it is very close to what's described in https://xmpp.org/extensions/inbox/muc-avatars.html

# Groupchat 1.0 usage statistics gathering

Groupchat 1.0 was probably the protocol that predated
[XEP-0045: Multi-User Chat] and there is still some compatibility that
lives on, in the XEP and in implementations.

This module tries to detect clients still using the GC 1.0 protocol and
what software they run, to determine if support can be removed. 

Since joins in the GC 1.0 protocol are highly ambiguous, some hits
reported will be because of desynchronized MUC clients

# Compatibility

Should work with Prosody 0.10.x and earlier.

It will not work with current trunk, since the MUC code has had major
changes.