Add DragCommand. Default Y/N on optional fields. Open/Save project items.

- More Y/N in Optional, making it easier to omit parameters.
- AT removed from Envelope, since T already gives it.

src/commands/PreferenceCommands.h

@@ -63,6 +63,7 @@ public:
    wxString mName;
    wxString mValue;
    bool mbReload;
+   bool bHasReload;
 };
 
 #endif /* End of include guard: __PREFERENCE_COMMANDS__ */