#251 Magic tool for drawing filled polygons

[William Kendrick]

A Magic tool that allows you to place 3 or more points on the canvas, and upon clicking the first point a second time, generates a polygon from the points, and fills it in.

Considerations:
* Each click or click+drag would draw a solid line; we could alternatively fill the shape (if it has 3+ points); however, it would be difficult to tell when the user is "done" with one polygon and wishes to begin a new one
* During drag operation, we should show guides denoting where each point is; possibly previewing the filled results (esp. if we do not fill it after each release; see above)
* We'd need to allow for some inaccuracy when trying to click the first point
* We could possibly offer a way to edit the other points

[William Kendrick]

Added to 0.9.33.