Interactive placement additions

Filter only ButtonRelease events before moving the 3x3 grid. Emacs for example, maps immediately if we ignore any event...

Mimic CTWM interactive placement features during the 3x3 grid move:
- clicking Button2 and dragging the outline will give the window its current position but allow the sides to be resized;
- clicking Button3 will give the window its current position but attempt to make it long enough to touch the bottom the screen;
- releasing any other button still position the window at the current position, as before.