Add ranks to set elements

[nichtich]

Add resource field rank with allowed values preferred, normal (default), and deprecated with same semantics as Wikbase data model (see Ranks in Wikidata).

Only one element of a set is allowed to have rank preferred. Default value is normal except for single-element sets the default value SHOULD be preferred. Applications SHOULD ignore elements of rank deprecated and choose element of rank preferred when selecting a single element of a set.

Example:

{
  "prefLiteral": [ {
      "literalValue": "Twix",
      "rank": "preferred"
    }, {
      "literalValue": "Raider",
      "rank": "deprecated"
  } ]
}