reset_problem in capa_module should always return dicts not strings

this is for the master branch (versus cms-master)

Make chem preview more robust

- give the preview div an id, use that to look it up instead of dancing around in the DOM

Feature/victor/capa ajax

Toggle shouldn't follow anchor

choicegroup should only process choices belonging to its input_id

Feature alex crystallography mitx

- I'm starting to vaguely understand js variable scope and closures.  Long way to go though :)

* still call the callback when skipping duplicate file.  This updates the completed flags, and so the overall "we're done" callback fires properly.

more removal of data("id") in favor of attr("data-id")

Fix to read utf-8 enconded html files for custom course tabs

address Ike's comments.

Feature/victor/capa ajax

I'm happy with all the changes to inputtypes, modulo the minor comments.
I didn't read chemcalc.py closely, but the tests look good.

- make chemical_equations_equal return False instead of raising errors.
- make tests not choke on unicode
- get full coverage

Hotfix/arjun/fix integer disc ids

styles and tiny bit of logic for community tas

- architecturally slightly questionable: the preview ajax calls goes to an LMS view instead of an input type specific one.  This needs to be fixed during the grand capa re-org, but there isn't time to do it right now.
- also, I kind of like having a generic turn-a-formula-into-a-preview service available

tweaked collapsible selector to target the proper section

add django management command for dumping grades to CSV file