RFC: Add cards relations

[Aviortheking]

{
  "id": "swsh1-1",
  ...
  "related": [
    { "type": "language", lang: 'fr', "card": { /* card brief*/  },
 
    { "type": "reprint", "card":... }
  ]
}

related is a list that include the type defining what the relation is, a card defining the link to the other card.

Other keys can be included depending on the need, like language include the lang key to indicate the language of the relation

Current types :

• next
• previous
• language
• original
• reprint