Negative Inventory not shown

[lubos]

Done.

[16.3.10] Added "Back order" column to "Inventory Items" tab for negative inventory

When inventory quantity goes negative, Manager will show new column called “Back order” on “Inventory items” tab to indicate how many items have been sold, written-off or consumed by production order without being able to be taken out of inventory yet. When new items are added into inventory, Manager will automatically process transaction in “Back order” column.