Filter by day responsibles on dashboard

In #4029 we implemented display of day responsibles on the dashboard, but no filter capabilities. In this issue here, we want to implement filtering by day responsible.

Ideas (pick and choose one or multiple):
1. Add a completely separate filter option for filtering day responsibilities
1. When filtering by combined responsibility, keep showing headers of days on which there are matching day responsibilities
1. On days where the combined responsibility filter hides some of the schedule entries, provide an option to temporarily re-show all schedule entries of this day (to get an overview of what's going on on a given day on which I am day responsible)
1. Make all day responsibility avatars partly transparent when they do not match the responsibility filters