Add mentor assignment to Sonar.

Review Request #7713 — Created Oct. 19, 2015 and submitted — Latest diff uploaded

Information

student-sonar
master
9a02884...

Reviewers

With this, we now can assign a "primary mentor" to each student. This will show
up in their main bio section, and each mentor will now get a "My Students"
section in the sidebar to quickly get to their assigned students.

Assigned mentors to each student and saw that everything worked as expected.