Messy first pass at a perseus API for mobile

Summary:
A rough first pass at an api for mobile and `onInputError` functionality

Adds apiOptions as an optional prop for ItemRenderer and Renderer,
and adds support for `onInputError`

Test Plan:
 * input-number:
    * made an input-number
    * entered "2--"
    * graded it
    * made sure i got an alert
 * expression:
    * made an expression
    * entered "2--"
    * made sure it gave me an alert after a couple seconds
    * made sure it gave me an alert on grading
 * checked correct/incorrect grading for both the above widgets (with
   "5" and "x+1" solutions respectively)

Reviewers: charlie

Reviewed By: charlie

Subscribers: alex, mgp, laura

Differential Revision: http://phabricator.khanacademy.org/D9387