thx to @dalf for the fix (#1365)

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.

closes issue #863

utils/fetch_languages.py gets languages supported by each engine and
generates engines_languages.json with each engine's supported language.

Use only one engine for the four search from Qwant

- Web
- Images
- News
- Social media