Barcode image should be displayed on the product page, not only barcode numbers.

Rationale:

• it becomes easier to test our mobile apps with products we don't have physically
• it becomes easier to compare Open Food Facts data with other mobile apps
• it makes data more trustable: I can verify the barcode of my product is the same as displayed on the web page
• some people, for whatever

Reviewing #159 I saw some odd behavior locally with plenty of credits left in proten... switched to master and the behavior is there too, so not introduced by 159, just happened to first notice while looking there

Adding one item to cart was (eventually) causing other items to show max-allowed... don't have time to find a clean/minimal reproduction, but likely a bug with recent JS changes to

We have CI for Open Food Facts to run tests on all repos. It could be nice to enable in the future.