Review CmdChangeAttribute constructors

[cecilios]

While documenting these commands some issues were raised and should be reviewed:

• There is a group of constructors using an specific object as target. This object is passed in the constructor. Is this necessary?
  Instead, use the object pointed by the cursor?
• There is another group of constructors without a target object. They seem to use as target the object pointed by the cursor.
  Is this necessary? Instead, use the objects in current selection?
• Bool attributes are not considered, but LenMus used bool attributes and stores them in int variables. Is this correct?
  Define an specific constructor for bool values?

[cecilios]

Closed. Time ago I used issues to track my TODO list. This is no longer the case and so I prefer to remove old issues I created.