Highlight region of interest

## Use Case

Requested by @MFarhadloo25: would like an alternative to the current ROI clipping that *highlights* the region of interest within the larger volume rather than clipping voxels outside the region entirely.

## Solution

This can either look like the volume outside the ROI persisting but becoming extra transparent, and/or a box appearing around the ROI. From @MFarhadloo25: "Either a box, or different transparency. Think of ROI as original image color, and remaining image with different alpha intensity"

Question: is opacity outside ROI and/or highlight box color configurable? Does that make this a UX issue?