A new PSR-14 event is added that allows to modify the categories to be
assigned to an event.
The event itself (including already existing categories) as well as the
list of categories to be used after import are available.
It is possible to change the categories to be assigned, e.g. keep some
of the existing categories.
That way it is possible for installations to add custom categories to
events.
Relates: #10623
Destination Data One provides an source info explaining where the data
originally came from.
This is now added to event records and exposed in TYPO3 backend.
That allows editors to check the source and contact corresponding
sources in order to fix broken data.
Relates: #10630
A new PSR-14 event is added that allows to modify the event right before
it is persisted within Destination Data One import.
This for example allows to alter dates, prices, etc.
Improve handling of missing end time in dates.
