Spawn Gunther's Visage (npc 5666) at end of quest 411

Script to run after completing quest 411 The Prodigal Lich Returns. C++ code by @kldxzzhc2 in  #12482
Modification: Added actual NPC text from http://www.wowwiki.com/Gunther_Arcanus .
Thanks for the good and helpful comments, just remember that you are talking to someone who doesn't even know how to write hello_world.cpp without having to Google it first). ;-)