Add remaining basic shapes and fix bug.

circle, ellipse, line and path shapes added with representative
default attributes. All shapes now have a transform variable.

The use of the constructor NewView in the render and update was an
unintentional closure, which has now been fixed by referring to it as
this.constructor instead.

	modified:   svgwidgets.js
	modified:   svgwidgets.py
	modified:   svgwidgets_example.ipynb