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

Check for None to fix 3.091 progress tab crash

- get_module() contract says it can return None (e.g. if access control check failed)

fixed default tolerance on numericalresponse

- for now, wraps existing render functions as separate classes
- a bit of cleanup in how it's called from capa_problem
- initial tests to make sure things are testable.

- give different errors when student or author stuff is messed up (I was seeing "No way to interpret '3' as a number" :P)
- preserve traceback in exception

Fix openid provider URL matching for usernames with non-word characters

Added an indicator on Progress page when there are no problem scores in a section.

Fix some issues with integer ids in the discussion forum

tweaked collapsible selector to target the proper section; functionality like this should have its own class to avoid selector conflicts, but it may be too late to fix this now

* Move tests into a separate file
* add a chemical_equations_equal function to compare equations, not expressions
* rename some internal functions with a leading _

Adding django-admin/rake command to set the staff bit

Don't function call on null