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 .
This is pure copy/paste from @kldxzzhc2 so I don't know more than that I wanted to follow up on your suggestion to put it in a PR so it could be discussed instead. What do you think of the MangosZero code I linked? Does that look like a better solution than this code from kldxzzhc2 ?