The itemNode and expandoNode elements have changed from img to
span (https://bugs.dojotoolkit.org/ticket/16699), so we now put our
tree icons inside them rather than replacing them.
Signed-off-by: Anders Kaseorg <andersk@mit.edu>
Somehow the image filters order matters for iOS browsers (Chrome, Safari), so
grayscale filter is not applied if -webkit-filter is not the last filter in
list.
