Account deletion (#3728)

* Add form for account deletion

* If avatar or header are gone from source, remove them

* Add option to have SuspendAccountService remove user record, add tests

* Exclude suspended accounts from search

app/views/auth/registrations/edit.html.haml

@@ -11,3 +11,8 @@
 
   .actions
     = f.button :button, t('generic.save_changes'), type: :submit
+
+%hr/
+
+%h6= t('auth.delete_account')
+%p.muted-hint= t('auth.delete_account_html', path: settings_delete_path)