Volume mesh inspector widget
Similar to #81 (closed) , but for unstructured grids: aeva should have an operation whose custom attribute-view creates a 3-D widget that uses crinkle clip or crinkle slice to display the interior of meshes. The operation's configure()
method should be overridden to detect when the set of associated entities is modified. When this occurs, the visibility of related surface entities should be turned off (or set to semitransparent or wireframe) and the widget's visual representation used instead (so that the interior of the volume is not obscured by surface).