GUAC-1126: Add client-specific disconnect action to menu. Style with danger.

guacamole/src/main/webapp/app/client/styles/client.css

@@ -117,4 +117,12 @@ body.client {
     width: auto;
     height: auto;
 
-}
+}
+
+.client .user-menu .options li a.disconnect {
+    background-repeat: no-repeat;
+    background-size: 1em;
+    background-position: 0.75em center;
+    padding-left: 2.5em;
+    background-image: url('images/x.png');
+}