feat: migrate web app manifest from JSON to webmanifest format and update mobile-web-app-capable meta tag.

Author: chaxus

index.html

@@ -6,7 +6,7 @@
     <link href="/img/64.png" rel="shortcut icon" />
     <link rel="manifest" href="./manifest.webmanifest" />
     <meta name="theme-color" content="#0052cc" />
-    <meta name="apple-mobile-web-app-capable" content="yes" />
+    <meta name="mobile-web-app-capable" content="yes" />
     <meta name="apple-mobile-web-app-status-bar-style" content="black" />
     <title>Document Editor</title>
     <script src="/web-apps/apps/api/documents/api.js"></script>