now appending .xml suffix when saving viewport, viewsettings and decals refs #36

git-svn-id: http://svn.code.sf.net/p/sumo/code/trunk/sumo@16654 29f149b2-0c63-11e1-8f5c-a347f6a9acd0
make gui more responsive when single-stepping refs #36

git-svn-id: http://svn.code.sf.net/p/sumo/code/trunk/sumo@16655 29f149b2-0c63-11e1-8f5c-a347f6a9acd0