Spawning of The Unforgiven (Stratholme) scripted

With this code The Unforgiven and its adds (Vengeful Phantoms) will
spawn when a player gets close to the elite's spawn point
Update stratholme.h
Update instance_stratholme.cpp
Update instance_stratholme.cpp
Merge pull request #261 from Chuck5ta/Rel20

[Script] Spawning of The Unforgiven (Stratholme) scripted