DlgEditClass Cancel needs to undo all edits

[hasii2011]

Mainly since we are working on a copy determine if before it started was the diagram in an unmodified state; If so set it back to that

[hasii2011]

Actually, just do not indicate that the model was updated unit the OK button in the top level Class

[hasii2011]

fixed on branch then merged to the 🤡 master 🤡 branch