Moved positions and sizes of close and shade buttons to Skin
changed buttons to use PixmapButton
moved buttons from PlaylistWindow to PlaylistWidget and PlaylistShade
removed now unused Button
fixed position of shadebutton (was off by 1)
fixed icon of shade button in shaded mode
Use the new PixmapSlider class which is based on Qt's AbstractSlider
class for sliders. This should also fix some offset problems in
PositionSlider which appeared after the introduction of the new Button
class
