Add support to embed widgets in the completion-list as discussed on the list. An additional related feature is implemented: Users can return html-strings on the role ItemSelected when an item is selected, and if they do, the size of the selected item will be increased and the text shown in the added space.

It will be reduced again once the next item is selected. This will be great for showing small and fast information like comments on functions. I've also got a qt-patch to make this efficient(currently qt repaints too much).