Added Source to Enterprise API Enrollments

Merge pull request #620 from edx/aj/ENT-2082_api

[MICROBA-56] Added Source to the EnterpriseEnrollments for Enterprise APIs

Sorted results of enterprise-learner API by active flag

Sorted results of enterprise-learner API by active flag in descending order so active enterprises are on the top

Better handling when Integrated Channels return unexpected results

Better handling when Integrated Channels return unexpected results

Added Source to Enterprise CourseEnrollment and Pending Enrollments

Added Source to Enterprise CourseEnrollment and Pending Enrollments.

ENT-2463 | Fix race condition that can occur in EnterpriseCustomerUser enroll method

Try and protect against race condition EnterpriseCustomerUser.enroll() method during course enrollments.

Added missing migration for EnterpriseCustomerUser

Added missing migration for EnterpriseCustomerUser

2.0.14

• Add Enterprise selection page to allow a learner to select one of linked enterprises

Add Order creation to enrollments

• Add manual order creation to enterprise manual enrollment admin form
• Update 'EnterpriseCustomerUser' model. Add 'create_order_for_enrollment'. Called during 'enroll'. Will create an ecommerce order for pending course enrollments.

Add management command to seed devstack LMS with sample enterprise data

Add management command to populate sample enterprise data in the LMS within devstack

Updated content metadata export for Cornerstone and Degreed

Updated image url field in the content metadata export for Cornerstone and Degreed.