Add match_language function in utils to match any user given
language code with a list of engine's supported languages.
Also add language_aliases dict on each engine to translate
standard language codes into the custom codes used by the engine.
languages.py can change, so users may query on a language that is not
on the list anymore, even if it is still recognized by a few engines.
also made no and nb the same because they seem to return the same,
though most engines will only support one or the other.
The currency names are fetched wikidata and store into a static file : searx/data/currencies.json
This file is loaded when the currency_converter is loaded.
A database is perhaps more appropiated.
