Feature Request: Ellipse tool for the graph tool

[dlglin]

I would like to have an ellipse tool for the graph tool. The only practical way I see it working is to plot the centre followed by one end of each of the axes. I don't know if it's better to force students to plot a specific axis first (e.g. they always have to plot the vertical axis followed by the horizontal axis). The case where they plot a circle would also have to be accounted for. Should this be allowed, or should they get some sort of warning/error.