enhviz): center the volume rendering around the visible area
Description
When cropping a volume rendered image either with the box widget or the freehand tool, the camera reset is centered around the bounding box of the whole image.
Functional specifications
Take the bounding box and the freehand crop into account for the computation of the camera reset.
Technical specifications
Change the bounding box/sphere of the proxy geometry accordingly.
Test plan
Test in SightViewer with an image.