Reorganised the redstone simulator

-> Many thanks to @worktycho for the idea, and @Haxi52 for the implementation plan!
* Uses classes and inheritance now
* Speed should be improved

src/ClientHandle.cpp

@@ -927,6 +927,12 @@ void cClientHandle::HandleBeaconSelection(int a_PrimaryEffect, int a_SecondaryEf
 
 void cClientHandle::HandleCommandBlockBlockChange(int a_BlockX, int a_BlockY, int a_BlockZ, const AString & a_NewCommand)
 {
+	if (a_NewCommand.empty())
+	{
+		Kick("Command block string unexpectedly empty - hacked client?");
+		return;
+	}
+
 	cWorld * World = m_Player->GetWorld();
 	if (World->AreCommandBlocksEnabled())
 	{