Added Polygon, Line Segment(s), and Ray subwidgets for Interactive Graph

Summary:
Polygon lets you choose 3-12 sides and exact, congruent, or similar matching.
Polygons are constrained to be simple (non self-intersecting).

Line Segment lets you match up to 6 (arbitrary number) line segments.
Ray matches a single ray.

Test Plan: Tested all subwidgets via test.html, including proper JSON representation.

Reviewers: alpert

Reviewed By: alpert

Differential Revision: http://phabricator.khanacademy.org/D3930