Section boxes should allow for break the same way as 2D crop regions.
This is not trivial as we need to consider what should be allowed: vertical breaks, horizontal breaks or both? In the most complex, and general form, of this new feature we should be able to cut the section box up like a Rubic's Cube so that each resulting sub-volume can be adjusted individually.
Introduction of this feature would allow for 3D visualisation of more complex volumes with omissions of less important spaces. Currently this can only be achieved by creating a number of 3D views, each with its own section box and then carefully assembling the views on a sheet. This is tedious and frustrating.
