fixed quantities on items import

I noticed that the csv import was still putting quantity into the items table, so I edited the item controller's do_excel_import() method to put the quantities into the item_quantities table.  

I also edited the import_items.csv file, deleting the Quantity and Location columns, and adding two new columns: location_id and quantity. 

You can add as many of these columns as you need.  For instance, if you have two locations, you can add these columns:

location_id: 1
quantity: 100
location_id: 2
quantity: 200