added work around for limits 2 error
Fixed again
Fix issue #33473, allow white space in expressions involving subtraction

13-2v or 13 -2v was being accepted, but 13 - 2v was not.
https://github.com/Khan/khan-exercises/issues/33473
Allow whitespace after negation and subtraction.

Add \\s* after all instances of [-\\u2212] in exercises and tested.
There is no reason for counting students wrong for variance in formatting
of this type, and it is not infrequent to see expressions as 5 - x in text.
var tag incorrectly terminated with a /span ending tag

This was causing errors on our local school server by
students with Macs using Safari.
Unrevert i18n stuff only in the i18n branch for now
i18n-ize some exercises

Summary:
i18n-ize inscribed angles exercises, indepdent probability, and identifying
points 1

Test Plan: View those exercises, notice that they're not horribly broken

Reviewers: eater, emily

Reviewed By: eater

CC: alpert

Differential Revision: http://phabricator.khanacademy.org/D2063
Switch to using expr() function and make more interesting prpblem
Fix solution entry box and make better range of problems
Write function to simplyify terms in sum of expressions
Split into separate + and - exercises to make it easier to deal with hints
Change method of generating problem to avoid questions that simplify
Simplify fraction where required
Add solution
Remove unnecessary variables
Avoid the rare chance that the two constants could be 0 and the coefficients share a factor
Start separating out interface code from khan-exercises

TODO: make local mode work again, separate everything else out

Test Plan:
Did problems in addition_1; took hints, lost leaves.
Saw that my perseus exercise doesn't make a failing HTTP request anymore.
Commented out exercise-content.js and saw that when loading a Perseus exercise, the only JS errors were from binding events in exercises.js and user-exercise-cache.js -- those'll be the next things I tackle.
Move other events to Exercises event bus

Test Plan:
Did problems in addition 1, took hints, saw leaves decrease, finished stacks, etc. and everything looked okay. ack "\bKhan\b" javascript/exercises-package/ gives nothing suspicious any more.
Move interface.js to within khan-exercises

(No other changes)

Test Plan:
Loaded Addition 1.
Split out most exercise interface code

There is no scenario in which this is not a bitch to review. Sorry.

TODO: make local mode work again
TODO: get rid of utils/hints.js and merge with exercise-package/interface.js

Test Plan:
Did problems in Addition 1 locally and took hints and saw buttons update and lost leaves.