Fix local mode by deferring jQuery-using init

Auditors: eater, cbhl
Fix double-typeset-after-clone MathJax tmpl bug

Test Plan:
Visited /exercises/divisibility.html?seed=131&problem=0&debug and saw 91, not 9191.

Auditors: eater, cbhl
Merge branch 'master' of git://github.com/Khan/khan-exercises into similar-triangle-2