v2.11.0

Added

• Add a default contract definition template without a branded logo
• Add filters for the admin viewset through the field created_on
  to search orders on exact date, before date, after date and range of dates.
• Add filter for admin order viewset by product type
• Add button in back office for refunding an order
• Add teachers, skills and certification_level fields
  to Productmodel
• Add admin api endpoints to CRUD Teacher and Skill resources.
• Add certification section in back office product detail view

Changed

• Update product endpoint to CRUD teachers, skills
  and certification level fields

Fixed

• Fix order update on archived course run