Added new nav icon in prep for dropdown list.

src/templates/slim/html5/_tools.html.slim

@@ -5,3 +5,4 @@
     i class="fa fa-plus-square" aria-hidden="true"
   / include _searchbox.html
   <input dir="auto" style="position: relative; vertical-align: top;" spellcheck="false" autocomplete="off" class="searchbox__input aa-input" id="doc-search" name="search" placeholder="Search in the doc" required="required" type="search">
+    i class="fa fa-navicon" aria-hidden="true"