Core/Realms: Realmlist refactors

* Removed global realm variable from World and use RealmList everywhere
* Match auth build key with client version
* Restored allowedSecurityLevel checks for realmlist packet building
* Restored updating population field
Port From (https://github.com/TrinityCore/TrinityCore/commit/c4b710446d62c95eb8124175203fa5f394912594)

Source/Game/Chat/Commands/MiscCommands.cs

@@ -1250,7 +1250,7 @@ namespace Game.Chat
 
             // Query the prepared statement for login data
             stmt = LoginDatabase.GetPreparedStatement(LoginStatements.SEL_PINFO);
-            stmt.AddValue(0, Global.WorldMgr.GetRealm().Id.Index);
+            stmt.AddValue(0, Global.RealmMgr.GetCurrentRealmId().Index);
             stmt.AddValue(1, accId);
             SQLResult result0 = DB.Login.Query(stmt);