remove item groups as they kill performance when zooming in/out
remove item groups as they kill performance when zooming in/out

namespace-ee/react-calendar-timeline,namespace-ee/react-calendar-timeline,meikoudras/react-calendar-timeline,mkawczynski07/react-calendar-timeline,mkawczynski07/react-calendar-timeline,mkawczynski07/react-calendar-timeline,signalwerk/react-calendar-timeline,signalwerk/react-calendar-timeline,meikoudras/react-calendar-timeline