Affects:
Choicegroups, option inputs, textline, and formula equation inputs

STUD-669.

keep log_event for compatibility

Change the `MathJax.Hub.Queue(initializeRequest)` to a simpler function call
(`initializeRequest.call(this)`). This was failing to give a proper context
to initializeRequest, and `this.value` was turning up as `undefined`.

Also add a fallback if we need to display some code before MathJax finishes
its original typesetting.

I was stubbing out `Queue` in my specs, so the tests had to be changed around
a little.

Named `FormulaEquationInput` (name up for debate)

- Based off ChemEqnIn
- Add FormulaEquationInput in inputtypes.py
- Add a call to a skeleton method for a preview

javascript:

- Queue up some MathJax
- Put some ordering on the AJAX requests: add a parameter when the request was started, when it returns check that it isn't outdated before displaying the preview
- Tests

Note: we moved the `jsinput` tests and DISABLED them, because they were causing the tests to fail.

When JS functions are defined with names, they are local variables, and inaccessible
if defined inside a closure. Django-Pipeline concatenates all of our JS into one
big closure. This function explicitly assings the function to a property of the
`window` object, so that it is accessible to other JS functions.

When JS functions are defined with names, they are local variables, and inaccessible
if defined inside a closure. Django-Pipeline concatenates all of our JS into one
big closure. This function explicitly assings the function to a property of the
`window` object, so that it is accessible to other JS functions.

Mocked loading of captions.
Fixed remaining tests in captions.
Fixed failing tests in speed control, and quality control. Turned off all VideoAlpha tests because browser crashes when all are run at once. To check that they are passing, go through each file one by one, replacing xdescribe with describe. Dont forget to change back to xdescribe when the test was run and turns out to be OK.
Some tests at the end of video_player_spec.js pass
Further fixing tests in video_player_spec file.
transfers changes to test_logic from master to __init__ and other files
Fixing more tests.

Change client-side code references from "delete" to "_delete". Some of these
were method names (or would generate method names), which breaks in IE8
because "delete" is a JavaScript reserved keyword. foo["delete"] is ok, but
foo.delete is not. This also makes forums marginally functional in IE8,
though the left-nav still has some display issues.