Inbound load planning workbench: add filter Vendor

The new feature New load planning workbench pages adds an inbound load planning workbench which is ca 3 times faster than the classic LPWB :-)

Often there are hundreds of suppliers, so it makes sense to only view the lines for a specific supplier.

Proposed addition: a filter box for the vendor ID (next to the existing filters for supply & demand filter, site, warehouse, ship and receipt date) would mean a giant step for better useability.

In this box, optionially enter a vendor account ID, or the first characters of the search key (same as when entering a new purchase order header).