Fetching Subsets (i.e bounding cubes) of a 3D Volume

[ilan-gold]

User story
Fetching a section of a 3D section based on a bounding cube would be useful both for navigation of larger volumes and localized viewing for any purpose.

Preferred solution
Add a bounds argument to the 3D layer for fetching and rendering only a given cube's worth of data.

Possible alternatives
We could also make this part of the loaders more tightly since the functionality already exists in 2D for geotiff.js (indeed we would rely on that for fetching the cube but we could wrap the 3D functionality in our own loaders).