Controller_Userguide: update typo, fix vars

Base description for some methods and properties.
`Controller_Userguide::$api` not used. 
`Controller_Userguide::after()`: route 'media' already setted in `Controller_Userguide::before()`, `$this->template->translations` not used.
@WinterSilence that just means there's no way it will ever fail === - so again, why is loose equals better? Does this change fix a bug? Allow a new feature? Achieve some other benefit?