This change makes it possible to update the scalar bar when the isodose level is changed. Isodose level is stored as the color name, and it can be changed in a color table view. Related issue: https://github.com/SlicerRt/SlicerRT/issues/8
I'm issueing a PR because there was a TBD there but also because I'm not sure what are the cases where color names might be changed in bulk, causing potential issues with lots of Modified events.