Edit scheduleEntry on activity view without redirection problem

[manuelmeister]

Now we have a better fallback for wrong/missing ids for activities and scheduleEntries. If a scheduleEntry is not found, but the activity is found, we load the first occurring scheduleEntry of the activity. If for whatever reason we can't find the activityId, then we try to find it using the scheduleEntryId.

This now also works if we navigate from scheduleEntry A to scheduleEntry B, then delete scheduleEntry A and use the browser back. Before this would just display our 404.

Replaces #4500

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[simfeld]

I don't understand it fully but something doesn't quite add up in the "browser back when previous schedule entry deleted" case: it finds another scheduleEntry of the activity, but some data is not refreshed properly. See screenshot where the title and time slot matches with a green LS entry but the badge says blue LP.

[manuelmeister]

@simfeld I've fixed the problem. Also some other edge cases where we don't execute requireActivityScheduleEntry (browser-back, activity switch, scheduleEntry switch)