Extbase will properly use mm sorting.
But categories can't be sorted within the TCA tree component.
Therefore it makes more sense to use actual sys_category sorting.
In order to do so, we add our own model and pass the sorting.
That way PHP can do the sorting.
That's the easiest approach.
Also events shouldn't contain to many categories. A performance impact
should not be high.
Relates: #8459
That has no effect, the info is just available from model.
This can be used to display a canceled date in a different way, or
render a notice.
Relates: #8092
Allow editors to select specific events to display.
Therefore add new necessary demand and setting for events and respect
them within repository.
Relates: #8092
Add new record type partner.
This can be something like a media partner or something else.
Allow an event to have zero or more partner.
Add necessary files and models with relations.
Relates: #8092
Allow editor to reference TYPO3 page records from events.
E.g. used to provide further internal information links.
Also those pages are resolved via DataProcessing.
That allows integrators to be 100% flexible to resolve those page info.
By default a menu is generated and media is resolved.
Also validation is ignored, as this improves performance and allows to
use the new class as injected property without validation fails.
Models are not managed via frontend and therefore don't need validation.
Relates: #8092
