Feature/edz/revert explicit charset

Fix missing import

adding explicit charset declaration to additional css

explicitly set the domain for the csrf cookie to match the session domai...

Force charset for application.sass to be UTF-8

refactor tests, add test for is_commentable_cohorted, fix a bug

Feature/victor/cohorts

Returns None if course isn't cohorted, even if cohorts exist.  Shouldn't happen on prod, but could if cohorting is turned off mid-course.

Conflicts:
	common/djangoapps/student/models.py

Add a .ruby-version file for use w/ rbenv

fix bug in video player:if from=xx:xx:xx is used then bkgrnd flashes

Pearson export/import code. (No merging before 25th Jan)

caveat: with a bit of hackery.  Need to do better testing once things are live.

min height on droppable areas and add padding to top/bottom on hover.

unit/subsection/section drag and drop on overview page