Implement basic keyboard navigation in Icons and Compact View

Things that are still missing:
1. Moving to the previous/next row with Up/Down in Icons View,
moving to the previous/next columns in Compact View.
2. Navigation in Details View.
Note that scrolling to the current item doesn't work yet, and
that the view does not have keyboard focus initially, so one has
to click the view before keyboard navigation and seleciton works.