Option to use jQuery icons in the toolbar

Option uiIcon added.
uiIcon should be set to a ui-icon name, i.e. ui-icon-pen, ui-icon-clock etc.

Example code: 
this.toolbarItems[0]= {
    tooltip: "Show more",
    uiIcon:"ui-icon-carat-1-s",
    click:  function() {
    // whatever
    }
};

Example picture
![sqdschema](https://f.cloud.github.com/assets/1586996/1786833/8f9a7b8e-68fb-11e3-9449-2b8d10b1dc94.jpg)