[jdt-ui-dev] Improving the UI for classpath setting

["Philippe Mulet" <Philippe_Mulet@xxxxxxx>]

After looking at UI preferences for formatting options, I thought that
build path preference could also show a picture of the resulting layout (as
the package view would show).

I think this could improve the user perception, especially when it comes to
dealing with source folders (you would show where packages start from
visually).