stitcher: allow user to provide an order and / or an approximate position
It would be convenient that users provide only a position (url --pos zzzz) or an order (option --preserve-order?) to give a first hint in case metadata are wrong.
case a position is given
tomwer z-stitcher first_scan.nx --pos z:1000 second_scan.nx --pos z:2000
This will overwrite scan positions
case an order is given
tomwer z-stitcher first_scan.nx second_scan.nx --preserve-order
this will overwrite the order and use the frame height for example to align scans