Added legacy grade export functionality to the instructor dashboard

[gsidebo]

What are the relevant tickets?

Closes mitocw#74

What's this PR do?

Adds legacy grade export functionality back into the instructor dashboard (was removed after the dogwood releases)

Where should the reviewer start?

Probably lms/templates/instructor/instructor_dashboard_2/grade_export.html and lms/static/js/instructor_dashboard/grade_export.js.

How should this be manually tested?

• Set the ENABLE_INSTRUCTOR_GRADE_EXPORT feature to True
• Set a REMOTE_GRADEBOOK_URL feature value - you can ask me or Peter for the proper setting here
• Navigate to the Export Grades tab for some course (eg: http://localhost:8000/courses/course-v1:edX+DemoX+Demo_Course/instructor#view-grade_export - make sure you have staff/admin privileges)
• Click the buttons and make sure they work

Any background context you want to provide?

This grade exporting functionality last existed in the dogwood releases (eg: dogwood.3-3) in something called the legacy instructor dashboard. As such there is a lot of functionality that was lifted out of the codebase as it existed then. I made several changes to match the patterns that currently exist in the instructor dashboard (the buttons make AJAX requests instead of submitting a general HTML form, etc.), but I tried to be careful not to overdo it with optimizing legacy code.

A few key files from the dogwood release that contained the legacy dashboard functionality:

• https://github.com/mitodl/edx-platform/blob/mitx/dogwood.3-3/lms/templates/courseware/legacy_instructor_dashboard.html
• https://github.com/mitodl/edx-platform/blob/mitx/dogwood.3-3/lms/djangoapps/instructor/views/legacy.py#L211

[blarghmatey]

@gsidebo when attempting to load this on the QA instances that are running the mitx/ficus-1rc1 branch it was throwing the following error:

    2017-06-05 12:32:19,403 ERROR 26686 [gunicorn.error] glogging.py:219 - Error handling request
    Traceback (most recent call last):
      File "/edx/app/edxapp/venvs/edxapp/local/lib/python2.7/site-packages/gunicorn/workers/sync.py", line 126, in handle_request
        respiter = self.wsgi(environ, resp.start_response)
      File "/edx/app/edxapp/venvs/edxapp/local/lib/python2.7/site-packages/django/core/handlers/wsgi.py", line 170, in __call__
        self.load_middleware()
      File "/edx/app/edxapp/venvs/edxapp/local/lib/python2.7/site-packages/django/core/handlers/base.py", line 52, in load_middleware
        mw_instance = mw_class()
      File "/edx/app/edxapp/venvs/edxapp/local/lib/python2.7/site-packages/django/middleware/locale.py", line 24, in __init__
        for url_pattern in get_resolver(None).url_patterns:
      File "/edx/app/edxapp/venvs/edxapp/local/lib/python2.7/site-packages/django/core/urlresolvers.py", line 401, in url_patterns
        patterns = getattr(self.urlconf_module, "urlpatterns", self.urlconf_module)
      File "/edx/app/edxapp/venvs/edxapp/local/lib/python2.7/site-packages/django/core/urlresolvers.py", line 395, in urlconf_module
        self._urlconf_module = import_module(self.urlconf_name)
      File "/usr/lib/python2.7/importlib/__init__.py", line 37, in import_module
        __import__(name)
      File "/edx/app/edxapp/edx-platform/lms/urls.py", line 11, in <module>
        from courseware.views.views import EnrollStaffView
      File "/edx/app/edxapp/edx-platform/lms/djangoapps/courseware/views/views.py", line 36, in <module>
        from lms.djangoapps.instructor.views.api import require_global_staff
      File "/edx/app/edxapp/edx-platform/lms/djangoapps/instructor/views/api.py", line 43, in <module>
        from lms.djangoapps.grades.new.course_grade_factory import CourseGradeFactory
    ImportError: No module named course_grade_factory

I assume this is due to that module being added in after the Ficus branch was cut from master.

[pdpinch]

Argh. Does this mean we've been working against the wrong branch?

[gsidebo]

Closing in favor of #9