- replaced all calls to commandManager.addCommand with firing of "newOperation"
events: this way any other element can listen to those events, increasing decoupling

- experimental : added removal of right hand operands for subtract boolean operations:
 does make more sense visually, but not too sure yet
- added handling of "newOperation" events generated by visual editor,
so that the content of these events (operations) can be added to command
manager, to add back undo-redo handling, in a decoupled way