Implemented writing off pattern fill style. This requiered special handling because the actual pattern images had to be written too.

So the KoShapeSavingContext now has functions to add the pixmaps and write them later to the odf store. I added a helper class KoShapeStyleWriter for handling the shape style adding and writing of the office:styles styles for convienience. Added a new StyleFillImage style type to KoGenStyle for fill-image styles.