Windows specific refactoring of Mouse3DController and RemovableDriveManager.

PrusaSlicer newly registers by Windows operating system for HID USB
plug / unplug notifications and for Volume attach / detach notifications,
and the background threads of the two respective services are waken up
on these Windows notifications.
The RemovableDriveManager also wakes up every 30 seconds to cope with
the drives ejected from Windows Explorer or from another application,
for example Cura, for which Windows OS does not send out notifications.

src/slic3r/GUI/MainFrame.hpp

@@ -141,6 +141,10 @@ public:
     wxNotebook*         m_tabpanel { nullptr };
     wxProgressDialog*   m_progress_dialog { nullptr };
     std::shared_ptr<ProgressStatusBar>  m_statusbar;
+
+#ifdef _WIN32
+    void*				m_hDeviceNotify { nullptr };
+#endif // _WIN32
 };
 
 } // GUI