title: Polymer Sub-menus templates?
body: <p>I wanted to create a submenu in Polymer 2.0. I used the app-drawer layout for creating a simple menu. Following is the code :-</p>
  
  <pre><code>&lt;app-drawer-layout fullbleed&gt;
        &lt;!-- Drawer content --&gt;
        &lt;app-drawer id="drawer" slot="drawer"&gt;
          &lt;app-toolbar&gt;Menu&lt;/app-toolbar&gt;
  
          &lt;iron-selector role="navigation" class="drawer-list" selected="[[categoryName]]" attr-for-selected="name"&gt;
                &lt;template is="dom-repeat" items="[[categories]]" as="category" initial-count="4"&gt;
  
                 &lt;a name="[[category.name]]" href="/[[category.url]]" &gt;[[category.title]]&lt;/a&gt;
               &lt;/template&gt;
          &lt;/iron-selector&gt;
          &lt;paper-menu&gt;
  
  
        &lt;/app-drawer&gt;
  
        &lt;!-- Main content --&gt;
        &lt;app-header-layout has-scrolling-region&gt;
  
          &lt;app-header slot="header" condenses reveals effects="waterfall"&gt;
            &lt;app-toolbar&gt;
              &lt;paper-icon-button icon="my-icons:menu" drawer-toggle&gt;&lt;/paper-icon-button&gt;
              &lt;div main-title&gt;[[title]]&lt;/div&gt;
            &lt;/app-toolbar&gt;
          &lt;/app-header&gt;
  
          &lt;iron-pages selected="[[page]]" attr-for-selected="name" fallback-selection="view404" role="main"&gt;
            &lt;my-view1 name="view1"&gt;&lt;/my-view1&gt;
            &lt;my-view2 name="view2"&gt;&lt;/my-view2&gt;
            &lt;my-view3 name="view3"&gt;&lt;/my-view3&gt;
            &lt;my-view404 name="view404"&gt;&lt;/my-view404&gt;
          &lt;/iron-pages&gt;
        &lt;/app-header-layout&gt;
      &lt;/app-drawer-layout&gt;
  </code></pre>
  
  <p>Is there an existing template in polymer 2.0 for building the sub-menu?</p>