Make connect button a regular <button>

It is a button, let the HTML element reflect that. And instead of
having the outer div being clickable, lets only make the inner one
work like a button. Because of that, this commit renames the outer div
to "connect_box" instead of "connect_button".

Note that we remove the disabled :hover-effect for touch on this button.
It doesn't make much difference since this button is one of a kind.

vnc.html

@@ -274,9 +274,9 @@
     <div class="noVNC_center">
         <div id="noVNC_connect_dlg">
             <div class="noVNC_logo" translate="no"><span>no</span>VNC</div>
-            <div id="noVNC_connect_button"><div>
+            <div id="noVNC_connect_box"><button>
                 <img alt="" src="app/images/connect.svg"> Connect
-            </div></div>
+            </button></div>
         </div>
     </div>