Window "keep-open"

WIP for a window wedge. It still has few issues:

1) Sometimes, if the wind pushes the window too much, the wedge falls down
2) it can only keep the window fully opened, there is no way of using this wedge to keep it half opened or so
3) it does only support horizontal opening (rotating axis vertical); some windows have a "vertical opening" (rotating axis is horizontal) and this wedge does not work in that case

You may upgrade it by finding or suggesting ways to fix the above mentions :)