The quick tile shortcuts have a feature of moving the window to the next
screen if one presses the same shortcut again.
E.g. if a window is quick tiled to the left on the right most screen,
quick tile again to left should move it to the left screen and quick tile
right. Thus it swaps the borders.
This wasn't handled correctly, especially not for modes like top and
bottom. If a window is quick tiled to the top an impossible mode was
generated: Left | Right. Doesn't make sense.
This change fixes the mode swapping and extends our quick tile testing
to cover the situation.