Transformer: Make the dilation circle always orange

Summary:
Makes the dilation tool always orange to indicate that it is a
handle with which to interact.

Test Plan:
 * Depends on khan-exercises D5570
 * Add a transformer
 * Click the dilation tool
 * Hover over it, unhover, move, and stretch it
 * Make sure it's always orange

Reviewers: alex

Reviewed By: alex

CC: alpert

Differential Revision: http://phabricator.khanacademy.org/D5578