Updated log visibility

In particular, ensure that ERROR is only used for errors that may affect
FreshRSS integrity, and ensure that feed errors are visible also in
production, i.e. visibility of WARNING
https://github.com/FreshRSS/FreshRSS/issues/885
https://github.com/FreshRSS/FreshRSS/issues/884

app/Controllers/authController.php

@@ -253,7 +253,7 @@ class FreshRSS_auth_Controller extends Minz_ActionController {
 				FreshRSS_Auth::giveAccess();
 				invalidateHttpCache();
 			} else {
-				Minz_Log::error($reason);
+				Minz_Log::warning($reason);
 
 				$res = array();
 				$res['status'] = 'failure';