add CourseTalk widget

cms/envs/common.py

lms/djangoapps/courseware/tests/test_course_info.py

lms/djangoapps/courseware/views.py

lms/envs/common.py

lms/static/sass/multicourse/_course_about.scss

lms/templates/courseware/course_about.html

lms/templates/courseware/info.html

openedx/core/djangoapps/coursetalk/__init__.py

openedx/core/djangoapps/coursetalk/admin.py

openedx/core/djangoapps/coursetalk/helpers.py

...edx/core/djangoapps/coursetalk/migrations/0001_initial.py

openedx/core/djangoapps/coursetalk/migrations/__init__.py

openedx/core/djangoapps/coursetalk/models.py

openedx/core/djangoapps/coursetalk/tests/__init__.py

openedx/core/djangoapps/coursetalk/tests/test_helpers.py