Add download counter for attached files

[elguitarraverde]

Summary

• add a downloads counter to attached files and show it in edit/list views
• increment the counter only for real downloads from MyFiles and ignore embedded preview requests
• cover the new Myfiles behavior with controller tests

esto lo cambio para que me pasen los tests porque en cli no funciona filter_input(INPUT_GET, 'myft')
$token = filter_input(INPUT_GET, 'myft');
$token = $request->query->get('myft');