US style nutrition list

[aleene]

There are some issues:

• [x] list is wrong -> I might have set it to the wrong list style
• [x] old and new us mixup
• [x] entering portion data as mg not working
• [x] vitamin A has no unit

[aleene]

Not sure this has ever worked well. I would like to allow the user to enter data per 100g AND per portion, but this is not allowed by OFF. So I should disallow it as well! When writing I should add the per variant that was used for editing. When reading I do not know what was the original value, so I will only use the standard value as processed by OFF. When editing a value, it should be saved as value and used for display later. If the user switches per, this value does not change. Ideally I should prohibit any per change after the first value edit. When saving this value with the per will determine how OFF processes the data. If the unit is changed, I should add the corresponding standard or serving as value.