Add ability to select and move the lines BETWEEN nodes

[joshusama]

What's the problem this feature will solve?
Right now if one wants to expand or shrink the area between nodes, both nodes have to be adjusted individually or more nodes need to be added in between.

Describe the solution you'd like
When you select the line between nodes, that segment turns red. This portion can be dragged and placed where desired (moves the nodes in tandem). This would also prevent whole polygons from moving when one accidentally selects a line and drags it (how it works now)

Innumerable ways this would help in the course of drawing, and a generally expected feature of many drawing tools (ITK-SNAP, for example)

Alternative Solutions

Just have to add more nodes or move more nodes, adding to ergonomic issues (and UX frustration)

LOW PRIORITY

[jcfr]

There is now support for interacting (rotate, translate) with annotation directly in Slicer. See below.

We would need to add support for scaling.