title: Adding tool-tip to an image rendered using Highcharts Renderer.image() api
body: <p>I wanted to add a tool-tip to an image that is rendered using:
  <code>image (String source, Number x, Number y, Number width, Number height) api</code>.</p>
  
  <p>I couldn't figure out a way to do this, I am using <code>org.moxieapps.gwt.highcharts</code> API's to
  create high charts in my GWT app.</p>