Fix validator, history, etc. for rotation_of_polygons

Summary: There's more improvements, but this is good enough for now and way better than before

Test Plan: Lots of testing locally including something with 180deg rotational symmetry (before the seeds changed, so I don't know of another seed to test now). Tested not answering, answering incorrectly, and answering correctly; ensuring the timeline showed everything correctly.

Reviewers: alpert

Reviewed By: alpert

Differential Revision: http://phabricator.khanacademy.org/D2135