Preference to handle the debug overlay, create fake classes to disable unwanted debug lines (for now)

Ideally this would also have an option to allow AutoSync,  AutoPlay, and Assist Tick with the debug overlay disabled, but that would require migrating that functionality elsewhere.

src/PrefsManager.h

@@ -334,6 +334,7 @@ public:
 	Preference<float> m_custom_songs_max_megabytes;
 
 	// Debug:
+	Preference<bool>	m_bDebugMenuEnabled;
 	Preference<bool>	m_bLogToDisk;
 	Preference<bool>	m_bForceLogFlush;
 	Preference<bool>	m_bShowLogOutput;