Revive Socrates

Summary:
Socrates was actually pretty healthy, he just had a few small misconfigurations of KathJax.  Also, I had to disable the automatic setting of socratesAvailable/socratesEnabled because:

```
// We used to set these to true automatically after the Socrates
// questions were loaded, but now we set them to the state they should
// be, before loading the questions (in
// video-addons.js~VideoPlayerModel._handleResults()).  We can do this
// because the video model has a "hasQuestions" attribute.  There is a
// small chance that the caller could set these 2 variables to true,
// and then this init fails.  There is currently no recovery path from
// that scenario, so it would probably result in some JS errors and
// would require a page refresh to fix.
```

I will link the review to the experiments shortly.

Test Plan:
Locally, hit these URLs:
/math/arithmetic/fractions/Equivalent_fractions/v/equivalent-fractions
/math/arithmetic/fractions/understanding_fractions/v/numerator-and-denominator-of-a-fraction
/science/healthcare-and-medicine/the-heart/heart-introduction/v/flow-through-the-heart
/science/physics/forces-newtons-laws/newtons-laws-of-motion/v/newton-s-1st-law-of-motion
/science/physics/forces-newtons-laws/newtons-laws-of-motion/v/newton-s-first-law-of-motion

Play around with the questions, they seem to be working.

Reviewers: desmond

CC: jace

Differential Revision: http://phabricator.khanacademy.org/D5224