ToDo left:
refactor `datetimes` property of `create-options-datetime` component to
not cause whole list to be updated. This is not only a performance issue
but also UX: e.g. validation state is lost when another item is added.
ToDo:
Label validation state should not be bound to validation state of first element (option)
but to validation state of all elements. If any element has an error label validation state
should be error. Only if all elements are fine, label validation state should also be fine.
