Support for XEP-0280: Message Carbons

Enable support for xep-0280
https://xmpp.org/extensions/xep-0280.html

This is very usefull. because if converse.js is loaded in multiple pages with the same jid, received messages will not be shown on all pages. we require XEP-0280 for this scenario to implement something like facebook chat or google hangouts etc.. .
Currently converse.js is only useful for single-page web applications. but most web sites are not single-page apps and the user may have a few tabs of the site opened at the same time.
we need XEP-0280: Message Carbons for this.

ejabberd supports this feature (in its master branch) by mod_carboncopy.

Note: You should use master branch of ejabberd to test this feature. because in previous versions, mod_carboncopy has a critical bug wich makes this module unusable. (including ejabberd 13.12)
Or you can compile only the mod_carboncopy and replace mod_carboncopy.beam file:
use this version (tested and works well):
https://github.com/processone/ejabberd/blob/2b527f5e9ae8ed867fc3b6c24f8b55f621e94663/src/mod_carboncopy.erl
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I have tested this and seems it's working properly.