Until we have a default style sheet implemented, set the default colors
to black text on white background for the root node, so that we don't
end up with unreadable black bars everywhere.
We match the following address bar behavior from Chrome and Firefox:
- When the address bar is clicked, select all text on mouse up if no
selection currently exists.
- On address bar blur, clear the selection.
The Calculator isn't functional yet, but when it eventually does work,
it will be helpful to not duplicate every number keypress when the
result input widget is focused. :^)
