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

Fix issue with unicode caracters in startpage : we shouldn't urlencode them if we are using POST.
Should fix #169. @dimqua can you confirm ?

* add language support
* remove not required code
* improve google-ad detection (no false detection anymore, I hope)
* other improvements

[fix] startpage engine : characters with diacritic were preceded by whitespace, and cleaner way to parse the result.