Add config flag to "force unit item" for inventory batch

tailbone/views/inventory.py

@@ -528,7 +528,8 @@ class InventoryBatchView(BatchMasterView):
             product = self.find_product(entry)
         if product:
 
-            force_unit_item = True # TODO: make configurable?
+            force_unit_item = self.rattail_config.getbool(
+                'tailbone', 'inventory.force_unit_item', default=False)
             if force_unit_item and product.is_pack_item():
                 product = product.unit
                 self.request.session.flash("You scanned a pack item, but must count the units instead.", 'error')