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.
@acoulton even if this is not possible now, it will be added later.