Improve presentation order of upcoming and live events

[owi92]

This adds a collapsible box to event blocks which hides upcoming events if there are more than one present. These events are ordered by their starting time so that the earliest upcoming event is shown first.
Presentation of the remaining events is also reorganzied so that live events are always shown before non-live events and all events are now ordered by their starting time instead of creation time.

Notes:

• The presentation order of the upcoming events is not configurable as I figured that we would always want to show the soonest one first, but that would be a small add if desired.
• I initially wanted to add some animation as the pop up of the details/summary element is a little sudden, but that turned out to be a little more complicated with that element because it doesn't have a fixed height, and also isn't super neccessary and might also look weird with too many upcoming events.

Closes #586

Edit: to test this, you need to either create some upcoming and live events or edit the status (is_live and start_time) of some events in the database.

[LukasKalbertodt]

I like it already and I think it's a big UX win. I have a few comments though.

The presentation order of the upcoming events is not configurable [...]

That's fine I think.

I initially wanted to add some animation [...]

Oh yeah the old problem of animating between height: 0 and height: auto. It's pretty annoying. The most common workaround recommended online (just use height: 8000) is bad and broken, and every other workaround is super involved and not worth it.

Edit: to test this, you need to either create some upcoming and live events or edit the status (is_live and start_time) of some events in the database.

Reviewers very much appreciate comments like this ;-)

[github-actions]

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Please resolve those so we can review the pull request.
Thanks.