Right-click menu on prim when material is assigned.
- Unbind Material should say Unassign Material

Right-click menu on any scope that matches the default scope name
- Bind Material menu should be removed
- Assign New Material should be changed to Add New Material

Right-click menu on material node when nothing else is selected
- Assign Material to Selection should be hidden, not just disabled, if there's no selection
- Bind Material menu should be removed
- Assign New Material: should you be able to assign a material to a material? This should be removed

Right-click menu on material node when there is a selection
- Assign New Material: should be removed

Letter-casing in Assign New Material sub-menus is incorrect
- USD instead of Usd
- glTF PBR instead of Gltf Pbr

Added unit test for the new "Add New Material" command.