Extend quick tiling to quarter of screen.

When moving a window to the upper or lower quarter of a screen edge the window will be quick tiled to the responsible quarter of the screen.

Moving the window to the middle half of the screen will do the normal quicktiling to half of screen, quick maximization at top screen is unchanged.

Thanks to Arthur Arlt for his first code contribution to KDE.
See Review Request http://reviewboard.kde.org/r/5661