Extrude mode refactoring (func. splitting, javadoc). Use constant directions for Ctrl-Drag.
See #8447: Add color and stroke customization to Extrude mode
fix stroke=1 0 0 exception (minor)

git-svn-id: http://josm.openstreetmap.de/svn/trunk@5741 0c6e7542-c601-0410-84e7-c038aed88b3b