Use an external transliterator to generate url's - fixes #662 and #349

This way, we have a unit tested, and popular library creating url's for us. It's used by behat and being integrated in doctrine extensions.
It also fixes #349 and #662 Greek, cyrilic and other characters will work again.

@note, not every Chinese or Japanese character is included in the character map yet, but it allready fixes all Russian, Greek,... characters.