Reload the page when the files app encounters an authentication error

This adds machine readable (non translated) error messages to `OC\JSON` and adds handeling of those error messages to the files app by reloading the page.
Reloading the page will handle authentication and token expired errors and shows a proper error messages in case the app is unavailable.

Fixes #9442 

cc @PVince81 @MorrisJobke 
missing whitespace: should be `'error' => 'unknown_user' )));`