1. P.O. fixes.
When entering the PO, user should choose application
specific UOM, instead of just write up something. So
basically unitperpack is the UOM id, and quantity is
the number of that unit ordered. In this way,
everything is consistant.
This involves several php files.
2. some related fixes such as billing, invoice, etc.
3. clean up customer update, add <tr><td> tag.