Add missing static assets (favicons, logos, webmanifest)

The static/ directory containing favicons, apple-touch-icons, logos,
robots.txt and site.webmanifest was not included in the repository,
even though app.html references these files. This causes missing
icons and broken manifest when building from source.

static/robots.txt

@@ -0,0 +1,3 @@
+# allow crawling everything by default
+User-agent: *
+Disallow:

static/site.webmanifest

@@ -0,0 +1,19 @@
+{
+  "name": "Dockhand",
+  "short_name": "Dockhand",
+  "icons": [
+    {
+      "src": "/android-chrome-192x192.png",
+      "sizes": "192x192",
+      "type": "image/png"
+    },
+    {
+      "src": "/android-chrome-512x512.png",
+      "sizes": "512x512",
+      "type": "image/png"
+    }
+  ],
+  "theme_color": "#ffffff",
+  "background_color": "#ffffff",
+  "display": "standalone"
+}