Allow global staff to generate example certificates
on the instructor dashboard.
Allow global staff to enable/disable self-generated
certificates for a course.
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
fix the quality issues and rebased with master
regenerated the migration file with a different number
i18n and verified te course mode
changes suggested by stephan
