Refactor answer-types to use Perseus-style scoring rather than the true/false/""/"..." mess

Summary: Doesn't change any functionality... yet... (hopefully)

Test Plan: Run http://localhost:8000/utils/test/answer-types.html and manually test answering correctly/incorrectly/unsimplified/empty for number, multiple choice, radical, multiple/set/checkbox combo, and custom in local mode.

Reviewers: alex

Reviewed By: alex

CC: alpert

Differential Revision: http://phabricator.khanacademy.org/D4225
Refactor the answer-types unit tests to validate the more descriptive scoring

Summary: This modifies the unit tests to more properly test the changes in D4225

Test Plan: http://localhost:8000/utils/test/answer-types.html

Reviewers: alex

Reviewed By: alex

CC: alpert

Differential Revision: http://phabricator.khanacademy.org/D4249
Move localeToFixed to khan-exercise.js

@alpert merged a pull request (commit 55a546bce5a806664eb9ab349684033335348aab) that added a use of localeToFixed in utils/answer-types.js. Since localeToFixed was defined in utils/math-format.js, it wasn't always available for all exercises. Moving it to khan-exercise.js so it's always available.

Test plan: Load an exercise that doesn't use math-format (addition_1) in local mode and observe there's no javascript error from answer-types.js

Auditors: alpert, csilvers
use localized decimals and fix #77031
use localized decimals
Merge pull request #78079 from mauk81/patch-3

use localized decimals and fix #77031
Merge pull request #78099 from mauk81/patch-4

use localized decimals
Merge branch 'master' into GH-71250
GH-71250 - Update nested validation to handle Perseus-style scoring change