visualizer: (fixes #72) Modify and use old configuration of CanvasEllipse

This patch fixes #72 (closed)

It reverts the configuration update made to src/visualizer/visualizer/core.py in commit 109f1f90 and modifies the usage of 'Goocanvas.LineDash' to 'Goocanvas.CanvasLineDash.newv'

This fix was suggested during GCI 2018 on the previous configuration of CanvasEllipse (before 109f1f90).