Yellow highlight in QML CollectionView component.

The delegate's background is forced to be transparent if current item.
The highlight is a light yellow rectangle. The horizontal separator
before the current item is set to a darker yellow color (shadow).
When the model emits the "modelReset“ signal, we set the view's current
index to -1. Add active focus trough mouse click in the Collection
component. Not sure if this is done right. Would be nice to have a nice
focus chain on <tab>.