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.
Then, sorry to be picky, those PRs should take it out. Otherwise if they don't get merged for any reason the TODO is gone too.