Add support for WIN key when setting group hotkey through GUI

As for AHK's hotkey control could not support WIN key, add a checkbox
to choose WIN key.
Change Single_Key_Show_Alt_Tab logic

In the past, it will sent Alt key's down and up event to simluate AltTab
logic. But it may cause a extra Alt key event.
Now it implement by testing specify flag "Single_Key_Show_Alt_Tab_Used".