It is now possible to use a single FillGeometry to fill objects that
are made of multiple filled objects (e.g. CustomShapes) so that
they look as using a single fill. This is used for CustomShapes,
but may later be 'extended' to be used for more cases. The basic
functionality was already in the primitives, but had to be added
to SDrObject due to these being used for CustomShapeVisualization
(currently - would be better to change this to primitives, too).

Change-Id: I1d9fb158191a9ec663e46f3911213be2f3d88986