add offline functionality by making this a PWA

- added favicons
- added manifest
- split javascript into main.js and elevators.js

manifest.json

@@ -0,0 +1,49 @@
+{
+  "name": "hvvstuhl.de",
+  "short_name": "hvvstuhl",
+  "start_url": ".",
+  "display": "standalone",
+  "background_color": "#030712",
+  "theme_color": "#047857",
+  "description": "Barrierefreie Aufzugs-Liste",
+  "icons": [
+    {
+      "src": "/icons/192.png",
+      "sizes": "192x192",
+      "type": "image/png"
+    },
+    {
+      "src": "/icons/512.png",
+      "sizes": "512x512",
+      "type": "image/png"
+    },
+    {
+      "src": "/icons/512-maskable.png",
+      "sizes": "512x512",
+      "type": "image/png",
+      "purpose": "maskable"
+    },
+    {
+      "src": "/icons/512-transparent.png",
+      "sizes": "512x512",
+      "type": "image/png",
+      "purpose": "monochrome"
+    }
+  ],
+  "screenshots" : [
+    {
+      "src": "images/screenshot-mobile.png",
+      "sizes": "430x900",
+      "type": "image/png",
+      "form_factor": "narrow",
+      "label": "Stationsliste"
+    },
+    {
+      "src": "images/screenshot-desktop.png",
+      "sizes": "1280x720",
+      "type": "image/png",
+      "form_factor": "wide",
+      "label": "Stationsliste"
+    }
+  ]
+}