[ADD] picking_line_description module v.7.0

Moving the MP: https://code.launchpad.net/~agilebg/stock-logistic-flows/adding_picking_line_description_7/+merge/219800
Hi,

Not really a fan of these types of ifs.  get_object_reference either returns None or a tuple.  Surely we can simplify this to just 

if ref:

All the extra defence seems a waste and there is a contract that this function will return only a tuple or None.