Use segment statistics routes in frontend

[fm3]

#7063 already introduced a route to query the volume of a segment in voxels.
(works only if a segment index is present, so currently only possible for tracings with no fallback segmentation)

More routes might follow.

It would be nice for the user to be able to access this information.

[dieknolle3333]

• Show Segment Statistics Button in group context menu
• this should open a modal with an Export as CSV, that downloads a CSV with segment id, segment name, segment size in nm, group name and group id
• also there should be a table in the modal, see mockup. needs to be scrollable, probably into both directions
• lastly the size should be an info row with the size in the context menu of the segments tab

see this slack conversation