Add endpoint to get managed courses

In this commit, the endpoint to retrieve managed courses for a specific user is created.

Changes look good

By Geert Habben Jansen on 2018-06-05T17:47:11 (imported from GitLab project)

merged

By Geert Habben Jansen on 2018-06-05T17:47:13 (imported from GitLab project)

mentioned in commit 871ee304

By Geert Habben Jansen on 2018-06-05T17:47:13 (imported from GitLab project)