…6616)

Current State (before this commit):

  Studio, as of today doesn't have a way to restrict a user to
  create a course in a particular organization. What Studio
  provides right now is a CourseCreator permission which gives
  an Admin the power to grant a user the permission to create
  a course.

  For example: If the Admin has given a user Spiderman the
  permission to create courses, Spiderman can now create courses
  in any organization i.e Marvel as well as DC.
  There is no way to restrict Spiderman from creating courses
  under DC.

Purpose of this commit:

  The changes done here gives Admin the ability to restrict a
  user on an Organization level from creating courses via the
  Course Creators section of the Studio Django administration
  panel.

  For example: Now, the Admin can give the user Spiderman the
  privilege of creating courses only under Marvel organization.
  The moment Spiderman tries to create a course under some
  other organization(i.e DC), Studio will show an error message.

  This change is available to all Studio instances that
  enable the FEATURES['ENABLE_CREATOR_GROUP'] flag.
  Regardless of the flag, it will not affect any instances that choose
  not to use it.

BB-3622

Signed-off-by: Farhaan Bukhsh <farhaan@opencraft.com>