Highlight relation or object when user clicks the list in Relation List, Selection List or Properties dialog
[ idea by Felis Pimeja ] + added HighlighHelper class 

git-svn-id: http://josm.openstreetmap.de/svn/trunk@6025 0c6e7542-c601-0410-84e7-c038aed88b3b
Merge branch 'master' into mirror