merge web app manifests (#708)

Right now here are 2 web app manifests:
- public/favicon/site.webmanifest
- public/manifest.json

But only the 1st one is referred in the html

This commit
- merged them into public/site.webmanifest (according to https://developer.mozilla.org/en-US/docs/Web/Progressive_web_apps/Add_to_home_screen#manifest, it should be in the root, whereas the spec suggests the `.webmanifest` extension
- complete the required fields

It now passes the Lighthouse PWA manifest test in Chrome

app/views/application/app.html.erb

@@ -10,7 +10,7 @@
     <link href="favicon/apple-touch-icon.png" rel="apple-touch-icon" sizes="180x180"></link>
     <link href="favicon/favicon-32x32.png" rel="icon" sizes="32x32" type="image/png"></link>
     <link href="favicon/favicon-16x16.png" rel="icon" sizes="16x16" type="image/png"></link>
-    <link href="favicon/site.webmanifest" rel="manifest"></link>
+    <link href="manifest.webmanifest" rel="manifest"></link>
 
     <link color="#5bbad5" href="favicon/safari-pinned-tab.svg" rel="mask-icon"></link>
     <meta name="theme-color" content="#ffffff">

index.html

@@ -15,7 +15,7 @@
   </link>
   <link href="public/favicon/favicon-16x16.png" rel="icon" sizes="16x16" type="image/png">
   </link>
-  <link href="public/favicon/site.webmanifest" rel="manifest">
+  <link href="public/manifest.webmanifest" rel="manifest">
   </link>
 
   <link color="#5bbad5" href="favicon/safari-pinned-tab.svg" rel="mask-icon">

public/manifest.json

@@ -1,25 +0,0 @@
-{
-  "app": {
-    "launch": {
-      "urls": [
-        "https://app.standardnotes.com/"
-      ],
-      "web_url": "https://app.standardnotes.com",
-      "container": "tab"
-    }
-  },
-  "offline_enabled": true,
-  "permissions": [],
-  "requirements": {
-    "3D": {
-      "features": []
-    }
-  },
-  "icons": {
-    "128": "favicon/android-chrome-192x192.png"
-  },
-  "name": "Standard Notes",
-  "description": "A Simple And Private Notes App",
-  "version": "1.0",
-  "manifest_version": 2
-}

public/manifest.webmanifest

@@ -0,0 +1,39 @@
+{
+  "app": {
+    "launch": {
+      "urls": [
+        "https://app.standardnotes.com/"
+      ],
+      "web_url": "https://app.standardnotes.com",
+      "container": "tab"
+    }
+  },
+  "offline_enabled": true,
+  "permissions": [],
+  "requirements": {
+    "3D": {
+      "features": []
+    }
+  },
+  "icons": [
+    {
+      "src": "favicon/android-chrome-192x192.png",
+      "sizes": "192x192",
+      "type": "image/png"
+    },
+    {
+      "src": "favicon/android-chrome-512x512.png",
+      "sizes": "512x512",
+      "purpose": "any maskable",
+      "type": "image/png"
+    }
+  ],
+  "name": "Standard Notes",
+  "description": "A Simple And Private Notes App",
+  "version": "1.0",
+  "manifest_version": 2,
+  "theme_color": "#ffffff",
+  "background_color": "#ffffff",
+  "display": "standalone",
+  "start_url": ".."
+}