Move ProjectWindowBase to new files...

... So that you can use GetProject without other linkage dependencies

src/ProjectWindowBase.cpp

@@ -0,0 +1,26 @@
+/**********************************************************************
+
+Audacity: A Digital Audio Editor
+
+ProjectWindowBase.cpp
+
+Paul Licameli split from ProjectWindow.cpp
+
+**********************************************************************/
+
+#include "ProjectWindowBase.h"
+
+#include "Project.h"
+
+ProjectWindowBase::ProjectWindowBase(wxWindow * parent, wxWindowID id,
+                                 const wxPoint & pos,
+                                 const wxSize & size, AudacityProject &project)
+   : wxFrame(parent, id, _TS("Audacity"), pos, size)
+   , mProject{ project }
+{
+   project.SetFrame( this );
+};
+
+ProjectWindowBase::~ProjectWindowBase()
+{
+}