Filter option for groups in participant folder

There are scenarios in which several groups are used in a course with the same group coach. When using the participant folder, the group coach sees all group participants of all groups. However, it is not possible for the group coach to see to which group the respective participants are assigned.

Therefore a filter for groups is implemented in the participant folder. 

FX Internal: book to https://office.bexio.com/index.php/pr_project/listMonitoring/projectId/13