docs: better PWA, more responsive, better description

docs/themes/navy/layout/partial/head.swig

@@ -3,8 +3,9 @@
   <title>{% if page.title %}{{ page.title }} | {% endif %}{{ config.title }}</title>
   <meta http-equiv="X-UA-Compatible" content="IE=Edge,chrome=1">
   <meta name="viewport" content="width=device-width, initial-scale=1">
+  <meta name="description" content="{{ page.description | default(config.description) }}">
   <link rel="dns-prefetch" href="https://cdn.jsdelivr.net/">
-  <link rel="manifest" href="/manifest.json">
+  <link rel="manifest" href="{% if page.lang != "en" %}/{{page.lang}}{% endif %}/manifest.json">
   <!-- Canonical links -->
   <link rel="canonical" href="{{ url }}">
   <!-- Alternative links -->

docs/themes/navy/layout/playground.swig

@@ -1,7 +1,8 @@
 <div id="playground" role="main">
   <div class="wrapper">
     <h1 class="inner">{{__('playground.title')}}</h1>
-    <div class="row inner">
+    <div class="loader" role=status aria-busy=true></div>
+    <div id="editors" class="row inner hide" aria-hide=true>
       <div class="col">
         <div id="editorEl">{{ raw('partial/demo.liquid') }}</div>
         <div id="dataEl">{}</div>