Scaladoc display on completion & showToolTip

integrated with completion and 'Show tooltip'/F2 (which is not exactly hovers)
pinging @sschaef  because he should see the ugly handover from `getHoverInfo2` to `getHoverInfo`
<< I'm open for ideas on how to improve it which do not imply rewriting the `HtmlProducer` in `Scaladoc`
I don't like the split up in this method. Please move the contents of `getHoverInfo` and `getHoverInfo2` to a new method (something like `createHoverContent`) that returns a `org.scalaide.core.internal.compiler.BrowserInput`. In `getHoverInfo` one can call `ret.toHtml` to get a string.