SdrObject: add meRelativeWidth/HeightRelation

Similar to Writer TextBoxes, this member is supposed to store the
"relation" (text::RelOrientation constants) of the relative
width/height, so far the layout always assumed "relative to page".

Change-Id: I5100745314e45ad322bff2b761e3722459aba014
sw: enable Relative{Height,Width}Relation UNO properties for shapes

Change-Id: I40080bd9b096b9fa5d660b11c4e5821db31fd412
SwAnchoredDrawObject: respect SdrObject::GetRelativeWidth/HeightRelation()

Change-Id: Ie107ea749a1f4c261106f0f18f3818b85d65e9b4