Fix links to jquery.ui and set proper default_image

* After commit ae5d3e2bb the links to jquery.ui becomes outdated.
* There is no `config.png` within `./web/images/` but on [preview of list](https://github.com/real-chocopanda/sfTwitterBootstrapPlugin/raw/master/doc/list.png) picture Config menu icon looks like `./web/images/gears.png`.