Add the scenario 'Manual product transfer' to the Shopfloor application.

This scenario allows to move a product or a lot from one location to
another location:

* scan the source location
* scan a product or a lot from this source location
* confirm or change the quantity to move
* scan the destination location

For developpers you will find a sequence diagram describing states and
endpoints relationships `here <./docs/manual_product_transfer_diag_seq.png>`_.
