Implement bounding boxes for Volumes, VolumeBounds

This MR adds an implementation for Bounding Boxes, particluarly, Axis Aligned Bounding Boxes (AABB). They're defined by a min and max vertex, and can link back to an entity that the bound around. Volume gains a method that returns a bounding box for the given instance.

These will be used for intersection tests in a later MR, but right now they only implement "intersect" with points (i.e. inside checks).