Update AdminLTE

- from 2.4.5 to 2.4.18 (cannot detect any issues)
- set default scancycle for Apple Devices to 1

front/img/manifest.json

@@ -4,7 +4,7 @@
     "display": "standalone",
     "icons": [
     {
-      "src": "",
+      "src": "https://net-dev.de/pialert_homescreen.png",
       "sizes": "180x180",
       "type": "image/png"
     }