CommandManager, MenuManager don't use Lyrics.h, MixerBoard.h ...

... instead define new base classes in src/commands that those other
windows can inherit.  The classes have nothing but a virtual destructor.  This
lets CommandManager use dynamic_cast to detect the special windows.

See commits cbfde23 and 68e4bf6 which added the #include directives

src/MixerBoard.h

@@ -24,6 +24,7 @@
 #include "widgets/AButton.h"
 #include "widgets/ASlider.h"
 #include "widgets/wxPanelWrapper.h"
+#include "commands/CommandManagerWindowClasses.h"
 
 struct TrackListEvent;
 
@@ -260,7 +261,9 @@ public:
 };
 
 
-class MixerBoardFrame final : public wxFrame
+class MixerBoardFrame final
+   : public wxFrame
+   , public TopLevelKeystrokeHandlingWindow
 {
 public:
    MixerBoardFrame(AudacityProject* parent);