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.

Replaced existing test_none_user_index_access_with_startdate_fails
test with new test now that the tested function has changed and
was causing the original test to fail.

Part of STUD-1030

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

BLD-465.

Co-author: Alexander Kryklia <kryklia@edx.org>
Co-author: Ned Batchelder <ned@edx.org>
Co-author: Oleg Marchev <oleg@edx.org>
Co-author: Valera Rozuvan <valera@edx.org>
Co-author: polesye
[BLD-384]

Co-author: Ned Batchelder <ned@edx.org>

This does not yet replace the existing per-student anonymous id, but
is intended to do so in the future.

Co-author: Alexander Kryklia <kryklia@edx.org>
Co-author: Ned Batchelder <ned@edx.org>
Co-author: Oleg Marchev <oleg@edx.org>
Co-author: Valera Rozuvan <valera@edx.org>
Co-author: polesye

Updates to depend on the latest version of XBlock, which includes
support for service-to-service (thirdparty) handler urls, which aren't
authenticated with a user (unlike handler requests coming from the
xblock client-side javascript).

Co-author: Ned Batchelder <ned@edx.org>

Also cleans up test_view_authentication to use user factories for
various user classes

remove field_data_cache from grades.grade and grades.progress_summary

cleans grading code by adding wrappers

remove field_data_cache from grades.grade and grades.progress_summary

cleans grading code by adding wrappers

This reverts commit 19dd49f3.

This centralizes the logic for group membership, and means that we
don't need to make queries to find out whether the legacy groups names exist.

remove field_data_cache from grades.grade and grades.progress_summary

cleans grading code by adding wrappers

add DOC_STORE_CONFIG to test settings

Adds xblock handler_url support to the LMS, and makes handle_ajax use
that code.

[LMS-230] [LMS-229]

* Changed text for "Are you sure you want to refund"...
* Addressed a CR comment adding clarity to student view code
* Converted UTC to pytz.utc