Fix (re-implement) answer distribution report generation.

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.

Add handler_url usable by descriptors

script bombs if comments include unicode

[LMS-1614]

Add acceptance test of image response

Add acceptance tests of GST module

Add acceptance tests of the conditional module

Add acceptance tests of Annotatable module

LMS: Use Open Sans Typeface via Google Web Fonts

Studio: Updating Google Font Syntax

Properly format errors/warnings.

Minor i18n improvements

Rename BlockUsageLocator's block_id field from usage_id

Set review timeframe more appropriately in contributing docs

Added JSInput template in Studio.

Added JSInput template to Studio and a sop attribute to JSInput. Only if it's set to false, as in JSInput's template, will JSChannel be used to bypass it. In all other cases (attribute not present or set to something else), SOP is enforced. Compatibility with jsVGL is therefore maintained. Multiple JSInput are supported in a vertical. Also, save button now functions. [BLD-523, BLD-556, BLD-568]

added detail about tolerance for numerical problems

and fix found errors.

Add a test for Django-based file uploads to problems.

Moving logme Require JS module out of individual XModules/Capa problems.

Added baseview(extended from backbone view), which can further extended ...

Add minor detail based on feedbback in training class -- use word
tolerance for margin of error, as that's what people searched on.  add
example for both percentage and numerical tolerance

Removing "logme" from comments.

BLD-608

Added Selenium page objects for LMS and studio

Rebalance acceptance test shards

Add baseview(extended from backbone view), which can further extended by other views + Add fucntion to modify iframe and embed tags + add related tests
STUD-823

Tweak language surrounding grade download button