Fix incorrect group status message
The message A supervisor should be invited so the group can be approved by the coordinator.
used to be shown as the group status explanation even when there are no roles which can be invited.
I changed the group status explanation logic so that a group is considered to have a coach when the course edition has no course-specific roles which students can invite. In that case, the Awaiting approval of the coordinator.
message is shown instead.
Closes #659 (closed)
Edited by Martin Mladenov