Core/DBLayer: Fixed possible crashes with async queries retrieving result

Closes #12655
Added comments to 6961f957c9d03bff634f0b75466458564845722e to make sure noone decides that storing the result in a variable is unneccessary
DB/Waypoints: Add Pathing for Garadar Wolf Riders in Nagrand
DB/Creature Formations: Fix formation error in last commit.
Removed OnQuestComplete hook, use QuestReward instead. Implemented OnQuestStatusChange hook

Also fixed some comments and added overrides
The OnQuestComplete hook was unused and didnt work properly