Add stock_picking_mass_assign

a module that allow to check the availability on a selection of delivery
orders, and an all the confirmed delivery orders by a scheduled action.
add translations to stock_picking_mass_assign
Sort pickings my min_date so they will be assigned according to
their expected date
Merge pull request #4 from guewen/7.0-stock_picking_mass_assign

Add stock_picking_mass_assign