* Rename methods that fetch a tray to prevent confusion
* Add methods to release a tray
* The Kardex method to fetch a tray has to send "0" in the carrier and
carrierNext field
* The pick and inventory screens release the tray only when there is no next
line, because the release is implicit when we fetch the next line,
the put screen releases everytime because the operator may take time
to start the next line and we don't know if they are going to scan a
next line or not.
* Exiting the screen or switching screen between put/pick/put-away has
to release the tray as well.
* Add vertical_lift_shuttle_id field on stock.location, help to find the
shuttle for a location
* Add StockLocation.fetch_vertical_lift_tray(), that needs to be
implemented in addons to send commands to the hardward to fetch a tray,
and if existing show a cell (laser pointer, ...)
* Add helpers on stock.move.line fetch_vertical_lift_tray_source() and
fetch_vertical_lift_tray_dest() that fetch the tray directly from a move
line's source or destination location
