Make scroll-to-current-day optional

[rixx]

We need a flag/prop to stop the widget from always grabbing focus. I think this is already alleviated a bit because we don't do it anymore if the event is not ongoing (TODO: check this), but even when the event is currently ongoing, not all websites will appreciate a scroll-to-schedule.

Will need to be a prop/flag, which pretalx will expose in the widget creator.