Feature request: Pivot manipulator/gizmo

[mortimerb]

Summary

A manipulator/gizmo to translate transformation pivot in the Viewer.

User story

What

Currently the only way to manipulate the pivot of a transform is to change the value of the pivot axes in the node editor manually. To have a manipulator/gizmo in the viewer to do so would be handy. This would also allow to use the snapping and targeting features on the pivot.

Feature proposal

This could be either it's own viewer tool (like translate, rotate and scale) or just a shortcut to switch between regular translation and pivot translation.

[mortimerb]

There was a follow-up question about this, in regards to the maintenance of the pivot translation.
There is apparently no need to maintain any of it further down the graph for now. So it's really just about a viewport manipulator to move the pivot interactively on an individual node - it's fine to reset the pivot position outside of the transform node.