[Product mode: view, edit...] Automatically load JSON data and cache it to allow more features

[CharlesNepote]

Cases where we should need to fetch json product's data:

• view mode: TODO: show issues on left side
  • lack of NS, NOVA, etc.
  • lack of ingredients but picture ok
  • lack of picture but ingredients ok
  • lack of picture and ingredients
  • presence of unrecognized ingredients
  • data quality issues
  • recent pictures but old data
• edit mode or view mode:
  • TODO: completeness (eg.0.9)
  • TODO: quality score based on:
    • nb of data quality errors
    • impact on Nutri-Score
    • https://world.openfoodfacts.org/data-quality-error/en:nutri-score-grade-from-category-does-not-match-calculated-grade
  • TODO: no fiber
  • TODO: old photos but new data
  • TODO: new photos but old data
  • TODO: popularity
• save product page to display some useful information such as "going further", etc.
  • addStateTags
  • addQualityErrorsTags
• version view: TODO: refactor flagThisRevision function
• version view: TODO: difference with previous version

See #66, #68 ...