Fix Mako templates to use latest request context

Fixed the edX middleware to lazily create request
context for Mako templates, so that it is based on
any changes made to the request object.

Verified that with this fix the "Instructor" tab is
correctly hidden when a staff member is viewing
the course as a student.
Support cohorting students via a CSV File.

TNL-735
add find_fixme task
Updating testing.md for find_fixme
Merge pull request #5961 from edx/dan-f/cohort-csv-upload

Upload CSV file for cohorting students
Merge pull request #6173 from edx/clytwynec/add_find_fixme_method

add find_fixme task
Merge pull request #6189 from edx/andya/fix-masquerade

Fix Mako templates to always use updated request context
Add DEFAULT_FILE_STORAGE configuration.

Tests in common are run with both CMS and LMS configuration (with different env files). Ensure the DEFAULT_FILE_STORAGE variables are in both environments.
Return the filename as returned from default storage's save.

It might be different from the requested filename.
Merge pull request #6215 from edx/christina/test-file-cleanup

Add DEFAULT_FILE_STORAGE configuration.
Adding yaml_config, a new settings module

This reads configuration directly from yaml
and imports it directly into settings
Merge pull request #6188 from edx/jarv/config-refactor-wip

moving defaults for yaml config out of common.py
WL-135 added the migration for the expiration_date field in the coupons model

added the functionality of adding the expiration date, and also handled in the shopping cart when the user try to add the expired coupon code in the shopping cart

added expiration date in the coupons list in the ecommerce page

added the unit tests and jasmine tests

added the api to create the course mode

bok-choy tests.

added the test cases for course_modes

added the form for the course modes

fix the quality issues and rebased with master

Renamed "add_honor_mode_to_course" to "add_mode_to_course" since we've removed the hard-coding.
Made the last "/" optional to avoid unnecessary redirection.