Highlight multiple segments of interest

[Albane-dlv]

Detailed Description

When working with a segmentation, there should be a way to highlight only relevant segments in the EM data. It could directly be used to create animations that play through a portion of the EM image stacks with appropriate tinting for only relevant segments.
Therefore, the user should be able to mark multiple segments as visible.

Context

When documenting things for publication or other presentation, a standard element of figure prep is to show single EM planes with tinted overlays of segments of interest. In these images, it is very helpful to be able to highlight only the relevant processes.

[hotzenklotz]

Fixed by #8281

[philippotto]

unfortunately, the issue itself is broader than #8281 and is meant to show a list of segments. I'll make this clearer in the pr description.