Fix: stop button css for all web browser

The stop button should follow all the attributes that the run button
has so it won't change the location when the play button becomes a stop
button.

The problem occurs in all browser since the buttons attributes has been chenged
in the last firefox compatiblity patch.

Signed-off-by: Bruno Bottazzini <bruno.bottazzini@intel.com>

client/css/app.css

@@ -318,11 +318,11 @@ iframe{
 .button_stop {
     background:url(../imgs/button_stop.png);
     background-repeat: no-repeat;
-    width:46px;
+    width:40px;
     height:45px;
-    position: relative;
     outline: 0;
-    display: inline;
+    margin-top: -10px;
+    margin-left: 5px;
 }
 
 .spin_sync {