substate khan-exercises

Test Plan: none
Add kray to test.html and testrender.html

Test Plan: none
Transformer: Fix angle grading

Test Plan:
 * Makea 90 degree angle and verify that a rotated version of it around
   its vertex so as to point in a different direction does not grade as correct
 * Make a 90 degree angle and verify that a rotated and reflected version
   resulting in the same angle does grade correct

Auditors: alex