Bounding boxes in 3D

[anaegel]

Bounding box only has only been implemented for triangles and quads in 2D:
https://github.com/UG4/plugin_TiffImage/blob/main/src/element_user_data.hpp

Need extension to 3D and enum ug::ReferenceObjectID

Element ROIDs are defined here:
https://ug4.github.io/docs/grid__base__objects_8h.html

[anaegel]

VertexIterators may be a smooth solution here:
https://ug4.github.io/docs/namespaceug.html#a1903407556f1e2b80c006ae920ea8e0e

[anaegel]

Check fd8e0e0 for a fix