To mark a language as dark-launched, add it to the DARK_LANGUAGES
django conf setting. To activate a dark-launched language, set he
query parameter `preview-lang` to the language code on any url.

[LMS-2045]
[LMS-2077]
[LMS-2076]

In Firefox YouTube video with start time plays from 00:00:00.
The reason was that seekTo() could not start playing a video from
a point that hasn't been buffered yet. Why this started happening
just now, really is hard to explain.

BLD-708.

STUD-1186

BLD-529.

Set default tolerance to 1e-3% for all responsetypes.

[LMS-226]
[LMS-2013]

Added sorting to the new pagination logic for STUD-995.

STUD-1072

These changes implement STUD-813. The commit consists of the
following logical changes:
 - a REST API has been implemented for a course's assets
 - the page itself now fetches the assets client-side
 - the Backbone.Paginator library is used to support pagination
 - the AssetCollection has been refactored to extend
   Backbone.Paginator.requestPager so that it can be paged
 - an abstract PagingView class has been added to generalize
   the communication with a paging REST API
 - the AssetsView has been reimplemented to extend PagingView
 - two new child views have been added:
   - PagingHeader: the paging controls above the list of assets
   - PagingFooter: the paging controls below the assets

This restores functionality that has been broken since the introduction of
XModuleDescriptor/XModule proxying (part of the XBlock transition). It generates
a CSV of all answers for all content of type "problem" in a given course, with a
row per (problem part, answer). The format is:

url_name, display name, answer id, answer, count

Example values:
  url_name = "7f1b1523a55848cd9f5c93eb8cbabcf7"
  display name = "Problem 1: Something Hard"
  answer id = i4x-JediAcdmy-LTSB304-problem-7f1b1523a55848cd9f5c93eb8cbabcf7_2_1
  answer = "Use the Force"
  count = 1138

Since it only grabs things of type "problem", it will not return results for
things like self/peer-assessments. Any Loncapa problem types will show up (so
multiple choice, text input, numeric, etc.)

Instead of crawling the course tree and instantiating the appropriate CapaModule
objects to grab state, this version draws directly from StudentModule. This lets
us skip a lot of processing and most importantly lets us generate the answer
distribution without causing side-effects (since XBlocks auto-save state). It
also lets us take advantage of a read-replica database if one is available, to
minimize locking concerns.

There are minor changes to the legacy dashboard around CSV charset encoding and
a change to OptionResponseXMLFactory to make it more unicode friendly. Answer
distribution output is now also sorted, to group together answers for the same
content piece.

Note that this does not introduce celery into the process. Answer distributions
are still only available for small courses.

This was originally created to fix [LMS-922], but it also addresses [LMS-811] and
possibly other areas in the legacy dashboard where CSV downloads break due to
character encoding issues.

BLD-564.

BLD-564.

Moving work on BLD-465 from PR 1811.
Fixing missing import clause in Python.
Addressing DB's comment.

BLD-465.

This applies to global staff (is_staff=True), not course staff.
Previously, staff were granted the Moderator role but not the Student
role upon enrolling in a course. If the Moderator role were later
revoked, then the user would have no role and be unable to post in the
forums, which is confusing for the user. edX staff indicated they would
prefer to not automatically receive the Moderator role, so the Student
role is granted instead. Note that staff will still be able to grant
themselves Moderator privileges through the instructor dashboard if
they wish.

JIRA: FOR-338