Allows Studendts to self select their groups with max user setting for each group. Includes also a "group assignment" mod

This includes two new features.
First: Students can now enrol themselfes in groups. Teachers can set up groups with enrolment keys, a lock-time (a point in time when a group schould become locked for joining and leaving) and a user limit. This feature also supports the new grouping feature.
The participants block was altered to offer a group overview for students where they can also join and leave groups.

In addition to that a new activity called "Group Assignment" was added, its the sam as a normal assignment, but if one group member uploads a file, than it is uploaded for every other groupmember. Grades are applied to every group member too. If a "Group Assignment" is created, one can select which groups schould participate. These are than saved in som extra database tables, so that if studendts change their group afterwards, it doesn't affect the group assignment created before.

A documentation (in german only, sorry) is included in the zip archive, as well as installation instructions in english

(This mod is still in development - fixing some minor bugs)