[TASK] Allow and replace special characters like umlauts

Currently ``<v:format.uri.sanitizeString />`` strips all special characters like umlauts which is not what one would expect. Open for discussion though is if this feature should be configurable via viewhelper argument.
Sure thing. What about an optional argument ``$replacements`` to add custom ones? If so, ``registerArguments()`` or ``render($string = NULL, array $replacements = array())``?