Define BasicUI::WindowPlacement and subclass for wxWidgets...

... An elaborate way to hold a wxWindow* as parent of a window, but avoiding
mention of wxWindow* in the member functions of BasicUI::Services, to be defined
next

libraries/lib-basic-ui/BasicUI.cpp

@@ -13,6 +13,8 @@ Paul Licameli
 #include <vector>
 
 namespace  BasicUI {
+WindowPlacement::~WindowPlacement() = default;
+
 Services::~Services() = default;
 
 static Services *theInstance = nullptr;