Modify AutoScreenMessage to keep map of all non-standard ScreenMessages.

This has a lot of advantages over the old ways.  Some of the initial ones are that
you can log a list of all screenmessages and their respective number and another
is that it would be fairly easy to add a reverse lookup, so you could get the name
of a ScreenMessage for log use by getting the ScreenMessage number.

stepmania/src/ScreenNetworkOptions.cpp

@@ -28,8 +28,8 @@ OptionRowDefinition g_NetworkOptionsLines[NUM_NETWORK_OPTIONS_LINES] = {
 	OptionRowDefinition( "Server",		true, "PRESS START" )
 };
 
-const AutoScreenMessage	SM_DoneConnecting;
-const AutoScreenMessage	SM_ServerNameEnter;
+AutoScreenMessage( SM_DoneConnecting )
+AutoScreenMessage( SM_ServerNameEnter )
 
 static Preference<CString> g_sLastServer( Options, "LastConnectedServer",	"" );