Added "Qty available", "Qty to be available" and "Qty to order" columns to “Inventory Items”

[lubos]

@eko

Forcing the use of Sales orders when managing inventory is not common

I’m only forcing to use sales orders if you want to track Qty to deliver. That’s all.

If you do not want or do not need to track Qty to deliver, then you don’t need to use sales orders.