Improve slicer util message boxes
Made messageBox show actual application name. "Slicer" application name was hardcoded before.
Also switched to using ctkMessageBox instead of QMessageBox to be able to have "don't show again" checkbox.
Made messageBox show actual application name. "Slicer" application name was hardcoded before.
Also switched to using ctkMessageBox instead of QMessageBox to be able to have "don't show again" checkbox.