Continued:

Continued:
- items may have own manufacturer, mostly then the product itself is an abstract
  product and does not have a direct manufacturer. Example: Milk can be made by
  many producers ("manufacturer", I known it isn't the same but here
  productProducer sounds a bit strange ...)
- bar code numbers might be very long, resulting an overflow of Long (!), so
  let's take String for now
- brand name of products happens very often in for example supermarkets
- manufacturer is now optional

Signed-off-by: Roland Häder <roland@mxchange.org>