Group filtering "drop-box" menu missing from workshop

Testing difficulty: Easy, but time consuming 1. Create a course with several groups and at least one grouping containing just some groups 2. Enable "Available for group members only" experimental feature 3. Create a workshop and let it be available for some grouping only 4. TEST: Make sure that only users from the selected grouping are listed at workshop participants listings (eg at the Assessment phase page, at the Manual allocation page etc.) [Previously, workshop displayed all users in the course] 5. Prepare another workshop with normal Visible groups mode 6. TEST: Make sure that everywhere where workshop shows a list of users (Grades report, Manual allocation page etc.) the groups selector is available and working and also the pagination widgets are available and working [Previously, group selectors did not work]