Add button in demo to toggle blockquote

Author: YoranBrondsema

assets/demo/index.html

@@ -58,8 +58,9 @@
         <div class="toolbar">
           <!-- Icons are from https://material.io/tools/icons/ -->
           <div class="toolbar-section">
-            <button data-action='toggleSection' data-args='h1'>Headline</button>
-            <button data-action='toggleSection' data-args='h2'>Subheadline</button>
+            <button data-action='toggleSection' data-args='h1'>H1</button>
+            <button data-action='toggleSection' data-args='h2'>H2</button>
+            <button data-action='toggleSection' data-args='blockquote'>Quote</button>
           </div>
           <div class="toolbar-section">
             <button data-action='toggleMarkup' data-args='strong'>