[OSK] Implement standard/enhanced keyboard handler (#1338)

- Add the respective standard keyboard resource.
- Implement the standard/enhanced keyboard dialog switcher.
- Implement save/load handler.
- Move the warning box conditinal check (bShowWarning) to wWinMain application entry point (this will prevent the modal welcome box from displaying each time the user switches into another dialog).

CORE-14428

base/applications/osk/main.h

@@ -24,6 +24,7 @@ typedef struct
     /* FIXME: To be deleted when ReactOS will support WS_EX_NOACTIVATE */
     HWND       hActiveWnd;
     BOOL       bShowWarning;
+    BOOL       bIsEnhancedKeyboard;
 } OSK_GLOBALS;
 
 /* DEFINES ********************************************************************/