#11 N3 form: show nicely URI buttons

[Jean-Marc Vanel]

In DataGUI, the "add URI" buttons should show either an icon related to the Class, property, or an meaningful name, or else a link icon.
The link buttons to "existing" URI's should show either an icon related to the instance individual, or fallback related to the Class, property, or an meaningful name typically the rdfs:label, or else the abbreviated URI as it is today.