fix #8483: option to reset preferences (Advanced preferences - More - Reset preferences)
+ big refactoring of advanced preferences editor (extracted PreferencesTable class with all table-related logic)

git-svn-id: http://josm.openstreetmap.de/svn/trunk@6021 0c6e7542-c601-0410-84e7-c038aed88b3b
Merge branch 'master' into mirror