Add problem history stub for Perseus exercises.

Auditors: eater, alpert
jQuery .trigger() expects extraParameters to be an Array

... when it isn't a plainObject.

Test Plan:
none, but this fixed the warning being uncloseable when I was mucking around with problem history.

Auditors: eater, alpert
Fix review nits

Fixes from rKEcbbd22da129cb8007ff95ff49fed08456856fa93.

Auditors: eater, cbhl
Remove custom stacks again again

Auditors: eater, cbhl
Revert "Revert "Don't use code tags""

This reverts commit c722dee724473e6cb3a37915f5890161a0a92cbc with a few fixes to make everything hopefully actually work.

Auditors: eater, cbhl
Two more code-script fixes

This is everything that uses Reprocess.

Auditors: eater, cbhl
Merge remote-tracking branch 'origin/master' into perseus
Expose Khan.mathJaxLoaded for Perseus to hook onto

Auditors: eater, cbhl
Basic Set Notation: typo (seperated -> separated)

Auditors: eater, alpert
Merge remote-tracking branch 'remotes/origin/master' into perseus
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
change referenced angle in hint. Fixes #43251
reorder angles of triangle in hint. Fixes #42454
Merge branch 'master' of git://github.com/Khan/khan-exercises into similar-triangle-2
Hide the timeline for Perseus problem history.

This is temporary; it's to avoid confusing users until it's implemented.

Test Plan:
locally, Chrome/OS X
- Viewed problem history for a perseus exercise and saw the timeline was gone.
- Viewed problem history for a framework exercise and saw it still worked.

Auditors: eater, alpert
Merge pull request #44085 from jedwood/similar-triangle-2

Solving Similar Triangles 2
Wait for base modules to load (i.e., MathJax)

Auditors: eater, cbhl
Break out framework-specific issue info

Auditors: eater, cbhl
Fix invalid CSS