Separate seasons-related code into extension

[carstingaxion]

Proposed NEW data modell (maybe version 1.0.0)

taxonomy ➡️ post_type ⬇️	post_tag	category	NEW wp_theatre_season_shadow
wp_theatre_prod	✔️	✔️	✔️
wp_theatre_event	🪢	🪢	✔️
wp_theatre_season	➖	➖	🔃

All this could also be done for Seasons, but I suggest separating all seasons-related code into an extension.

Everytime I created websites for theater-companies or solo-artists, without an own physical stage, seasons were not needed at all. For all houses with own and/or guest artists, seasons were a strict need. It's a 50:50 thing, if website-owners need seasons-handling.

When we have a working plan for how events relate to productions, we can go on here.

[slimndap]

Agreed. Seasons are hardly being used in my experience. Some theaters usesit to create a hidden page with all events for the next season. This allows them to preview all event contents, without publishing it on the website.