allow to call SimplifyWayAction with a custom threshold

git-svn-id: http://josm.openstreetmap.de/svn/trunk@6411 0c6e7542-c601-0410-84e7-c038aed88b3b
make "Tools" action types known from plugins

git-svn-id: http://josm.openstreetmap.de/svn/trunk@6412 0c6e7542-c601-0410-84e7-c038aed88b3b
undo/redo: param check + javadoc

git-svn-id: http://josm.openstreetmap.de/svn/trunk@6413 0c6e7542-c601-0410-84e7-c038aed88b3b