Obsidian Sanctum implementation (#752)

OS+2 implemented.
- Kill Vesperon before fight
- Mark Main Tank in raid interface

Offtank still needs a bit of work, and dps needs to stop running around once they're safe. But it's usable currently.
I think this should probably work for OS+1 and OS+0 with no changes but I was more concerned about implementing +2.

src/PlayerbotAI.cpp

@@ -1603,6 +1603,9 @@ void PlayerbotAI::ApplyInstanceStrategies(uint32 mapId, bool tellMaster)
         case 608:
             strategyName = "wotlk-vh";      // Violet Hold
             break;
+        case 615:
+            strategyName = "wotlk-os";      // Obsidian Sanctum
+            break;
         case 619:
             strategyName = "wotlk-ok";      // Ahn'kahet: The Old Kingdom
             break;