Allow to add prices of products without barcode

[raphael0202]

Problem

Currently, we cannot add the price of a product without barcode (products such as fruit/vegetables that are sold per kg or per unit).
It would be great to add it!

For the record, it's available on the web version of Open Prices.

[monsieurtanuki]

@raphael0202 We're blocked because in off-dart and Smoothie we're only able to autocomplete labels (e.g. 'Tomate'), and we don't retrieve the matching tags (e.g. 'en:tomatoes') and we don't have a way to retrieve the tags from the labels.
In Prices you want the tags...

[monsieurtanuki]

@raphael0202 @teolemon Besides, that means we cannot do that offline one way or the other.
Perhaps a decent minimal map of {tag: label} with standard fruits and stored locally would help.

[raphael0202]

I think it should be added to the autocomplete API on Product Opener. But we can definitely add support for language-specific tags on Open Prices side.

[monsieurtanuki]

@raphael0202 I don't know which solution is more pragmatic. Meanwhile, we're blocked here at Smoothie.