- updated "maintenance hint" with new release information v1.4.1

- improved "maintenance hint" rendering, toggle visibility by HTTP response header

app/main/controller/api/system.php

@@ -173,6 +173,9 @@ class System extends Controller\AccessController {
                 if($cacheSystem){
                     $f3->set($cacheKey, $graphData, $ttl);
                 }
+            }else{
+                // server cache data exists -> client should cache as well
+                $cacheResponse = true;
             }
             $graphsData[$systemId] = $graphData;
         }