Move the wrapping logic to get_item_rects(). This makes mouse events
able to hit the wrapped labels, and various other little things stop
glitching out as well.
Also, instead of having a per-line width when wrapping icon names,
make the text rect wide enough to fit every line.
IconView now responds to the editing key (F2) if the view is editable.
It does feel a little bit weird to have content_rect() return the text
rect for an item, and not the whole item rect. This internal API could
probably be better.
This implements the following optimizations:
* Rather than clearing a HashTable of selected items and re-populating
it every time the selection rectangle changes, determine the delta
by only examining the items that might be in the area where the
selection may have changed compared to the previous area. Then
only add/remove selection items as needed.
* When painting, only query and paint the items actually visible.
Also, keep a local cache of item information such as calculated
rectangles and selection state, so it doesn't have to be calculated
over and over again.
If selecting in a large icon view, and dragging the mouse outside
of the widget, or close to the border of it, start scrolling
automatically. This allows for selecting large amount of items
that exceed the amount that can be displayed.
