image uploading & render markdown

common/static/js/vendor/Markdown.Editor.js

common/static/js/vendor/customwmd.js

common/static/js/vendor/jquery.ajaxfileupload.js

lms/djangoapps/django_comment_client/base/urls.py

lms/djangoapps/django_comment_client/base/views.py

lms/envs/common.py

lms/envs/discussionsettings.py

lms/static/coffee/src/customwmd.coffee

lms/static/coffee/src/discussion.coffee

lms/templates/discussion/index.html

lms/templates/discussion/thread.html