Allow the choice of a group when manually enrolling a user

During manually enrollment, allow users to be registered in a group.

Currently :

1. Select the users to be enrolled manually
2. Select their role
3. Validate the enrolment
4. Go to the group management page
5. Add users to the group

Expected :

1. Select the users to be enrolled manually
2. Select their role
3. Select a group
4. Validate the enrolment