Refactor: Move more string related methods to StringConverter

MenusHelper::linkStringToArray() -> StringConverter::linkStringToArray()
MenusHelper::urlToLinkString() -> StringConverter::urlToLinkString()
Refactor: Extract visibility_path handling to a reusable class
Use boolean type for routing prefix values
Enable linkStringToArray to parse querystring
Teach VisibilityFilter to use querystring
Support UTF-8 or encoded UTF-8 in linkString