Allow to use a query block inside a label

[carstingaxion]

Use a gatherpress-query-block to provide label templates per production with the next date & venue already pre-filled from the query.

[carstingaxion]

Seems to work already

At least for identical, not on-going labels.

[carstingaxion]

Could use a switch for

1. Identical labels based on the first result
2. Different labels based on the full query. Which means, to reuse the calculated amount of labels as the request count of posts.