arc with axes, fix implode undo, minor fixes

20141211 replace2.py merged in replace.py by adding Params
20141211 circle via ellipse.py
20141211 various comments, including stdin section for each modified scripts
20141212 fix deletion order in OsmData.py
20141213 Params in arc.py for axes, "Arc with axes" command
20141213 tagcalc and arc2 icons