[josm_elevationprofile] Code cleanup

git-svn-id: http://svn.openstreetmap.org/applications/editors/josm/plugins@29960 b9d5c4c9-76e1-0310-9c85-f3177eceb1e4
[josm_elevationprofile] Added zoom button; update/layout track combo correctly

git-svn-id: http://svn.openstreetmap.org/applications/editors/josm/plugins@29961 b9d5c4c9-76e1-0310-9c85-f3177eceb1e4