Box implicit function was specified using a transform relative the data
bounds which were not exposed in the UI. This made it extremely tricky
to specify the box using absolute position/orientation/scale parameters.
Fixed that.

By default, now the box is always placed using absolute values i.e.
relative to a unit box anchored at origin. Added a mode that enables
user to provide an explicit bounding box to use for reference instead.
This will make it possible to support legacy state files.