Improve code block copy text

- Use JS to get it directly from the code block instead of needing a
  separate `pre.code-raw` to get it from. That makes it possible to:
- bashsession: Don't copy prompt or command output

layouts/_default/_markup/render-codeblock.html

@@ -1,13 +1,15 @@
+{{ $type := "text" }}
+{{ with .Type }}
+    {{ $type = . }}
+{{ end }}
 <div class="code-block">
     <div class="code-header">
-        <span class="code-type">{{ .Type }}</span>
+        <span class="code-type">{{ $type }}</span>
         <a class="code-copy-button">
             {{ i18n "copy_to_clipboard" }}
         </a>
     </div>
-    {{/* a div.highlight is already created by highlight function */}}
-    {{ highlight .Inner .Type }}
 
-    {{/* for copy to clipboard */}}
-    <pre class="code-raw" style="display: none;">{{ .Inner }}</pre>
+    {{/* a div.highlight is already created by highlight function */}}
+    {{ highlight .Inner $type }}
 </div>