* Adds option to add events lasting multiple days with adding an 'event_end_date' field

TODO:
* Translations

* Adds tax_query to components/project/events.php again as it was lost during coding
* Should fix the sorting order of events:
The array now checks (event_date >= today) OR (event_date < today AND (event_end_date >= today OR event_end_date =""))
Hoping thats how it should be

* Change & improve meta_queries and sorting in components/project/events.php, components/views/veranstaltungen.php & pages/single-veranstaltungen.php
* Changed "Veranstaltungsreihe" to "Aktion" for to leave place on elements/card-veranstaltungen.php to be able to display long date (like '30. September - 30. September) and still use qp_date
* Changed and added "Uhr" as it looks and feels more natural and use translations all over