Respond to pull request comments

  Clicking on any of the bars displays a list of students for that
  particular action (either opened the subsection or attempted the
  problem).
  Students are listed for the sub-sections.
  Students, grade and percent are listed for the problems.
  The on-screen list displays only the first 250 students with
  an overflow message if there are more students than that.
  The csv download lists all students.

Added test and cleaned up code formatting
Review based changes
Converting class method and attributes to private

LMS-2429

LMS-2262

LMS-2357

Changed "Status Page" -> "Page".

UX:
    support for displaying built-in tabs
    restored drag and drop on Studio Pages
    additional styling for fixed state on Studio Pages
    add a new page action added to bottom of Studio Pages

Dev
    changes for viewing tabs in studio,
    refactored the tab code,
    decoupled the code from django layer.
    is_hideable flag on tabs
    get_discussion method is needed to continue to support
external_discussion links for now since used by 6.00x course.
    override the __eq__ operator to support comparing with
dict-type tabs.

Test
    moved test code to common,
    added acceptance test for built-in pages
    added additional unit tests for tabs.
    changed test_split_modulestore test to support serializing objects
that are fields in a Course.

Env:
    updated environment configuration settings so they are
    consistent for both cms and lms.

LMS-2244

LMS-2346

LMS-2307

LMS-1287

LMS-1287

LMS-1203

In addition to email addresses. LMS-1438

LMS-2327

We would like to be able to generate arbitrary reports and expose them to the instructor by simply uploading them to S3.  The existing grade download infrastructure pretty much supported that already, however, all of the internal and external structures were referring to the reports as exclusively grading related.

Fixes: AN-590

LMS-2327

Metrics tab shows student data:
  -Count of students opened a subsection
  -Grade distribution per problem

for each section/subsection of the course.

Implemented for both the old and beta dashboard
Controlled by a feature flag 'CLASS_DASHBOARD'
Data is aggregated across all students
Aggregate data computed from courseware_studentmodule

STUD-1151

add a test case for enrollment caps

pep8 fix

Make XBlock client-side runtimes proper classes, so that handlerUrl can
be defined in a per-runtime way, and we can have multiple runtimes on a
single page.

[LMS-1630][LMS-1421][LMS-1517]

fixing unit tests

fixing merge error

fixing xqueue submission issue with unicode url (trial 0.1)

fixing fotmats as commented upon

removing yaml file language selection

Unicode changes to support QRF

removed unnecessary pass in modulestore/init.py

fixing merge error

fixing fotmats as commented upon

removing yaml file language selection

fixing pep8 violations

- fixing pylint violations

pylint violation

fixing line spaces and formats

ignore pylint E1101

remove empty line

fixing pylint violations

 pep8 violations

bulk mail unicode/decode

fix migration error

fix pep8 just to push again

more unicode/decode
Final changes to comments and error messages.

The submission time is serialized into json and sent to xqueue. Previously the
whole json body argument to send_to_queue() was being matched. Sometimes the
time calculated in the test would differ slightly from the time calculated in
send_to_grader() and the test would fail. This fix tests individual fields of
the body argument to mock_send_to_queue() instead.

STUD-1006