[mod] wordnik: convert to answerer (#4980)

Wordnik is now an answerer and not in the infobox anymore: it uses the
translations answerer, because it provides all the features needed. By default,
only its first results is shown

Additionally a new "define" category is added - I know, it's the same as the
"dictionaries" category, but I don't think we can alias categories.  This allows
to search e.g. for `!define tree`, the idea is to allow easy searches for
definitions of words.

Related:

- https://github.com/searxng/searxng/issues/4111

searx/settings.yml

@@ -2494,8 +2494,7 @@ engines:
 
   - name: wordnik
     engine: wordnik
-    shortcut: def
-    categories: [dictionaries]
+    shortcut: wnik
     timeout: 5.0
 
   - name: woxikon.de synonyme