re add the Urlization to allow custom transliterators

The urlization of slugs has been removed previously (https://github.com/l3pp4rd/DoctrineExtensions/pull/493/files#L9L224), just adding it again.

This is probably due to confusion on what Transliteration (changing from non alphabetic characters to latin alphabet characters) and Urlization (making the text url friendly) are.

As the default transliterator takes care of urlizing the text, this works for most people, but not if you need to set your own transliterator. In that case, transliteration and urlization have to be 2 separate steps.