DB/SAI: The Battle of Valhalas Quest Chain

Fixes #8377
Consists of:
1) Battle at Valhalas: Fallen Heroes (13214)
2) Battle at Valhalas: Khit'rix the Dark Master (13215)
3) Battle at Valhalas: The Return of Sigrid Iceborn (13216)
4) Battle at Valhalas: Carnage! (13217)
5) Battle at Valhalas: Thane Deathblow (13218)
6) Battle at Valhalas: Final Challenge (13219)