Add support for more than 4 joystick buttons under MSW

Use polling thread instead of relying on MM_JOYXXX events to allow
receiving events from all the supported buttons.

See https://github.com/wxWidgets/wxWidgets/pull/942

Closes #1142.

include/wx/msw/joystick.h

@@ -13,6 +13,8 @@
 
 #include "wx/event.h"
 
+class wxJoystickThread;
+
 class WXDLLIMPEXP_ADV wxJoystick: public wxObject
 {
   wxDECLARE_DYNAMIC_CLASS(wxJoystick);
@@ -22,6 +24,7 @@ public:
    */
 
   wxJoystick(int joystick = wxJOYSTICK1);
+  virtual ~wxJoystick();
 
   // Attributes
   ////////////////////////////////////////////////////////////////////////////
@@ -84,7 +87,8 @@ public:
   bool ReleaseCapture(void);
 
 protected:
-  int       m_joystick;
+  int                   m_joystick;
+  wxJoystickThread*     m_thread;
 };
 
 #endif