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.

nid/pref cookies are also removed

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.