Modify roi() server-side function so that it is more flexible in the kinds of arguments it can use

This ticket originate from which was a Bug ticket - that the roi() function didn't work with '3-d arrays.' Actually, it would work fine with those if the bbox was 3-d as well. But it was being called with a bbox that really didn't make much sense.

became: Build a new function that can combine bboxes to make a new, higher dimension bbox.

This ticket is: modify roi() so that it can apply that bbox to data.

Given a bbox of N dimensions, apply it to Arrays of N, N-1, ..., 1 dimension. Some design work may be needed to figure out, for the N-1, ..., cases which dimensions of the bbox should be used. Maybe based on names? Maybe based on dimension order?