Add support for terms of service

This feature is optional. It is based on the presence of a
`data/tos.html` file that an administrator can create. If this file
exists, FreshRSS will automatically add a "ToS" checkbox on the
registration page that users must check to be able to create their
account.

app/Controllers/authController.php

@@ -205,6 +205,7 @@ class FreshRSS_auth_Controller extends Minz_ActionController {
 			Minz_Error::error(403);
 		}
 
+		$this->view->show_tos_checkbox = file_exists(join_path(DATA_PATH, 'tos.html'));
 		$this->view->show_email_field = FreshRSS_Context::$system_conf->force_email_validation;
 		Minz_View::prependTitle(_t('gen.auth.registration.title') . ' · ');
 	}