* feat: Uses mod_external_services supporting urn:xmpp:extdisco:2.

The old mod_turncredentials.lua is left to continue working for those using old installs.
New install will start using the new module which will no longer be needed with prosody 0.12.

https://hg.prosody.im/prosody-modules/file/4841cf3fded5/mod_external_services/mod_external_services.lua

* squash: Updates ljm to support urn:xmpp:extdisco:2.