Add a small delay to barcode reading preventing accidental buying

[ConcernedHobbit]

The barcode scanner reads numbers into the interface quite quickly, even from small movements. I accidentally bought two Tupla Maxis just by holding it above the barcode scanner a half second too long.

Consider also whether this should be the case for different barcodes. Currently the only always-scanning barcode reader is pointed up, making it harder to scan two different barcodes accidentally. However keeping the handheld scanner held down and swinging it can cause accidents too.

It's nice to be able to read in multiple products quickly, but the use case for such rapid reading is probably rarer than accidentally reading the same product multiple times.