show/hide button interactivity

web/app.html

@@ -18,6 +18,7 @@
     <input id="additemid" type="text" placeholder="item id" pattern="[0-9]*">
     <input id="addattributes" type="text" placeholder="attributes (comma separated)" pattern="[0-9a-zA-Z, ]*">
     <button id="addbutton" type="button">Add</button>
+    <button id="global_toggleshow" type="button">show_hidden</button>
 </div>
 
 <!--popup confirmation window-->