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.
What wrong style - where does it say an if condition has to be all on one line? Though to be fair I'd prefer to see this extracted to a sensibly-named protected method, there's far too much going on to see what is being done here.