Hide After Due setting for Timed Exams

TNL-4366
Changes in studio to allow the hide_after_due setting to be utilized.

Includes:
    -python changes to contentstore, where the data is stored.
    -refactoring of timed-examination-preference-editor.underscore, to add this
        setting and make the editor more accessible.
    -javascript changes to link the new setting to the correct data model.
    -sass updates to fix a11y issues on the editor modal.
    -addition of post-due visibility information to course outline in studio.
    -new tests: python, js, acceptance, and a11y

common/test/acceptance/tests/studio/test_studio_settings.py

@@ -3,6 +3,9 @@
 Acceptance tests for Studio's Setting pages
 """
 from __future__ import unicode_literals
+import os
+
+from mock import patch
 from nose.plugins.attrib import attr
 
 from base_studio_test import StudioCourseTest
@@ -508,3 +511,63 @@ class StudioSettingsA11yTest(StudioCourseTest):
         })
 
         self.settings_page.a11y_audit.check_for_accessibility_errors()
+
+
+@attr('a11y')
+class StudioSubsectionSettingsA11yTest(StudioCourseTest):
+    """
+    Class to test accessibility on the subsection settings modals.
+    """
+
+    def setUp(self):  # pylint: disable=arguments-differ
+        browser = os.environ.get('SELENIUM_BROWSER', 'firefox')
+
+        # This test will fail if run using phantomjs < 2.0, due to an issue with bind()
+        # See https://github.com/ariya/phantomjs/issues/10522 for details.
+
+        # The course_outline uses this function, and as such will not fully load when run
+        # under phantomjs 1.9.8. So, to prevent this test from timing out at course_outline.visit(),
+        # force the use of firefox vs the standard a11y test usage of phantomjs 1.9.8.
+
+        # TODO: remove this block once https://openedx.atlassian.net/browse/TE-1047 is resolved.
+        if browser == 'phantomjs':
+            browser = 'firefox'
+
+        with patch.dict(os.environ, {'SELENIUM_BROWSER': browser}):
+            super(StudioSubsectionSettingsA11yTest, self).setUp(is_staff=True)
+
+        self.course_outline = CourseOutlinePage(
+            self.browser,
+            self.course_info['org'],
+            self.course_info['number'],
+            self.course_info['run']
+        )
+
+    def populate_course_fixture(self, course_fixture):
+        course_fixture.add_advanced_settings({
+            "enable_proctored_exams": {"value": "true"}
+        })
+
+        course_fixture.add_children(
+            XBlockFixtureDesc('chapter', 'Test Section 1').add_children(
+                XBlockFixtureDesc('sequential', 'Test Subsection 1').add_children(
+                    XBlockFixtureDesc('problem', 'Test Problem 1')
+                )
+            )
+        )
+
+    def test_special_exams_menu_a11y(self):
+        """
+        Given that I am a staff member
+        And I am editing settings on the special exams menu
+        Then that menu is accessible
+        """
+        self.course_outline.visit()
+        self.course_outline.open_subsection_settings_dialog()
+        self.course_outline.select_advanced_tab()
+
+        # limit the scope of the audit to the special exams tab on the modal dialog
+        self.course_outline.a11y_audit.config.set_scope(
+            include=['section.edit-settings-timed-examination']
+        )
+        self.course_outline.a11y_audit.check_for_accessibility_errors()