Namely, the pick/put/inventory operations are now split in
different models.
Pick and Put share a model and customize their behavior, which is pretty
similar. The inventory operation will have a different view and
different workflow.
This changes will ease a lot the customization of the different
workflows and views.
* 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
