When asked for icons or other images, we usually need to pass an ImageDescriptor (a reference to the image). We simply need to invoke ImageDescriptor.createFromFile() where the first argument is a class that is to be used as the root folder containing the relative path passed as a second argument.
Note: there is a /icons folrder in CVS and a /src/seg.jUCMNav/icons folder. The one used by the above actions is the second, the first is simply to allow our plugin.xml to see icons when developing (the ones loaded are in the second folder). (At least that's what I think.)
If we ever start creating static instances of images instead of creating them using ImageDescriptor, we should invest some time in creating central convenience methods that return an Image from a certain model element class or instance. That way, we'll have a central location to assign which icons go with which types. The palette, outline and other views could use these icons directly.