SelectFileWidget: Use gray for hover and @progressive-fade for drop active
SelectFileWidget: Use gray for hover and @progressive-fade for drop active

Follows up Ifb62d3a70cd71923c074607ad73e7397575361c1

Change-Id: I7a70374d89902e7afc3b5f6bc135fe91a84cc904

wikimedia/oojs-ui,wikimedia/oojs-ui,wikimedia/oojs-ui,wikimedia/oojs-ui