Bug1119: Windows menu on Mac should list all project names...

... Reimplemented without making dependency cycles.

Project and ProjectFileManager publish events for change of active project or
change of a project title.

WindowMenus.cpp can listen for those events, so that it can update the menu
appropriately.  So it's all done nonintrusively in the rest of the code.

src/Project.cpp

@@ -19,6 +19,7 @@
 #include <wx/frame.h>
 
 wxDEFINE_EVENT(EVT_TRACK_PANEL_TIMER, wxCommandEvent);
+wxDEFINE_EVENT(EVT_PROJECT_ACTIVATION, wxCommandEvent);
 
 size_t AllProjects::size() const
 {
@@ -111,6 +112,7 @@ void SetActiveProject(AudacityProject * project)
    if ( gActiveProject != project ) {
       gActiveProject = project;
       KeyboardCapture::Capture( nullptr );
+      wxTheApp->QueueEvent( safenew wxCommandEvent{ EVT_PROJECT_ACTIVATION } );
    }
    wxTheApp->SetTopWindow( FindProjectFrame( project ) );
 }