title: How may I reset the view of a canvas in tkinter?
body: <p>When I draw a rectangle in the canvas I know its coordinates, absolute (canvasx(), canvasy()) and relative (the ones that I have passed).
  Then, I may be able to move the canvas using the canvas scan_mark() and scan_dragto() methods.
  How may I return to the original position (before one or more of these scan_mark()/scan_dragto() calls) in order to re-center the rectangle of which the user might even have lost the position?
  Is there any reset view command/method? How may I keep track of the change that has occurred?</p>