Couple of Changes/Additions to .ORBX material Editor

[itsallgoode9]

1. Please, add an Undo option when working in the ORBX nodegraph.

2. Please add an option to "Keep un-connected nodes when Graph Editor is Closed"--Currently all unconnected nodes are deleted

When working in the nodegraph editor, I frequently am temporarily working with "test" materials (a lot of times I do this this with a basic glossy or diffuse to make it easier to see my procedural pattern, or how roughness map is affecting things etc). Sometimes, I'll accidentally close the window (or maya crashes) while my temporary material is applied and there is no way to get my old materials back other than to restart maya.