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

Engines:
 * Bing images
 * Flickr (noapi)
 * Google
 * Google Images
 * Google News

nid/pref cookies are also removed

TODO check other engines too

This allow to send request to google.* (according to the search language).
Before this commit, request in other languages than english was sent to www.google.com which was redirected to www.google.*
The PREF is still use on the www.google.com domain.

Sometimes there is two requests to google (depending of the source IP) : one to google.com, the second to google.fr (for instance).

Going to https://www.google.com/ncr and saving the PREF cookie for future use prevent this (there is no redirection).

But, recently (or not ?), by doing this the search returns English results even if the Accept-Language is specified.

There is still a way to prevent this : going to preference, set the search language. I don't know if this can be done by searx.

For now, a quick fix is to disable the use of the PREF cookie when the search language is not English (google engine will slower but returns excepted results).