STUN + XMPP ICE implementation.
Allows lobby players to host games without having to configure their router.
Differential Revision: https://code.wildfiregames.com/D364
Patch By: fcxSanya.
StunClient based on code by SuperTuxKart, relicensed with approval of the according authors hilnius, hiker, Auria, deveee, Flakebi, leper, konstin and KroArtem.
Added rfc5245 (ejabberd) support, a GUI option, refactoring and segfault fixes by myself.
Tested By: user1, Sandarac, Sestroretsk1714, Vladislav, Grugnas, javiergodas
Partially Reviewed By: leper, Philip, echotangoecho