[mod] update currencies.json and fetch_currencies.py

use a sparql request on wikidata to get the list of currencies.

currencies.json contains the translation for all supported searx languages.

Supersede #993

searx/search/processors/online_currency.py

@@ -20,6 +20,8 @@ def name_to_iso4217(name):
     global CURRENCIES
     name = normalize_name(name)
     currency = CURRENCIES['names'].get(name, [name])
+    if isinstance(currency, str):
+        return currency
     return currency[0]