Encrypt the session id before writing to tracking logs.
Also use md5 for constructing key for hmac.
Update ddt to 0.8.0
Extract i18n strings from *.underscore files using django-babel-underscore
Add additional tests for tracking of sessions.
Extract i18n strings from *.underscore files using django-babel-underscore

Change strings from mako.po into underscore.po, which is finally merged into djangojs.po.
Merge pull request #3971 from louyihua/django-babel-underscore

Django babel underscore
extract from underscore files under cms, lms, and common

to avoid extracting from test_root and such
Don't search for underscore files under lms
Babel underscore extraction update according to @nedbat

1. Add underscore.po into the merge section in config.yaml
2. Using one babel command template to construct two babel commands
Merge pull request #3988 from louyihua/django-babel-underscore

Babel underscore extraction update according to @nedbat
Text Annotation Tool: Added Instructor Filter and Clear Search
Video Annotation Tool: Added Instructor Filter
Image Annotation Tool: Added Instructor Filter
Image Annotation Tool: Annotation Mode for AB Testing

Annotation Tools PR Fixes

- forgot to overwrite the previous line
Reformats markdown problem templates avoid extra line breaks.
Annotation Tools: PR Fixes

- Fixed camel case for variable name
- Fixed indentation in imageannotation.html
- Changed all mentions of Instructor Username to Email
- Turned annotation_mode into phrase
- Fixed indentation in imageannotation.html
- Added comments in imageannotation.html

- Changing annotation_mode in OSDA
Fixes spelling of Michigan in template.
Add support for search spell corrections to Forums UX.

Co-authored-by: Brian Talbot <btalbot@edx.org>

JIRA: FOR-591
Merge pull request #3986 from edx/jsa/search-spell-correction

Add support for search spell corrections to Forums UX.