Underline quick help button key accelerator (h).

IPython/frontend/html/notebook/templates/notebook.html

@@ -57,7 +57,7 b''
         <button id="save_notebook"><u>S</u>ave</button>
     </span>
     <span id="quick_help_area">
-      <button id="quick_help">QuickHelp</button>
+      <button id="quick_help">Quick<u>H</u>elp</button>
       </span>
     <span id="kernel_status">Idle</span>
 </div>