[Commands] Modify #grid and #wp. (#1399)

- #grid add will no longer let you put in a duplicate grid.
- Grid nodes now spawn with invul/immune to damage.
- Grid nodes now set an entity variable "grid_id" on spawn.
- This allows grid nodes to be specifically despawned by "grid_id" entity variable, meaning you can view multiple grids at once and not despawn them all accidentally.
- #grid hide will despawn your targeted NPC's Grid nodes.
- #grid add, #grid show, #grid delete, and #grid hide send messages to let GM know what's going on.
- #wp add and #wp delete now send messages to let the GM know what's going on.
- #wpadd now send messages to let the GM know what's going on.

zone/entity.cpp

@@ -5314,3 +5314,12 @@ int EntityList::MovePlayerCorpsesToGraveyard(bool force_move_from_instance)
 
 	return moved_count;
 }
+
+void EntityList::DespawnGridNodes(int32 grid_id) {
+	for (auto mob_iterator : mob_list) {
+		Mob *mob = mob_iterator.second;
+		if (mob->IsNPC() && mob->GetRace() == 2254 && mob->EntityVariableExists("grid_id") && atoi(mob->GetEntityVariable("grid_id")) == grid_id) {
+			mob->Depop();
+		}
+	}
+}