make a standard training / test / verification data set

[alexgarel]

If we want to be able to verify our progress we need to have standardized set of products.

Build a list of products (list of barcode):

• A first list should be used to be used for training / test sets (we can have a standard split, but this should be also used for cross training with different train / test split)
• A second list should be used for validation (it's always the same)

However the sets should be built accounting for the different features present in data. So there should be some balancing in training / test / validation set for data having the different modalities : title / ingredients / nutritional data / images / OCR.

depends on

• Create new dataset #10