Always set parent for the Dialog, if we want to see the Dialog in the same display as a parent.
Dialog will be shown in the primary monitor otherwise.
+ fixed a draw of the canvas legend when we move application between Retina and non-Retina displays
Fixed layouts after the second opening of the dialog.
(Removing any extruder from the sequence does not cause an incorrect layout)
Validation of entered values added
(0 is not a valid value)
