Allow querying for species

[egonw]

Narrower than #15 is to allow certain kinds of "restriction (per line https://github.com/blinry/wikidata-cardgame/blob/master/cardgame.js#L401) and it would be nice to have a card game for, say, honey bees or sharks. The restriction would look like as on the second line:

SELECT ?item ?itemLabel ?image WHERE {
  ?item (^wdt:P171)+ wd:Q30034 .
  ?item wdt:P18 ?image .
  SERVICE wikibase:label { bd:serviceParam wikibase:language "[AUTO_LANGUAGE],en". }
}