When merged this pull request will:

• No longer require seats to inherit from Thing. This allows mods (including other components in ACE) to define classes inheriting from e.g. Static to be seats.
• Add a safeguard to FUNC(addSitActions), so if it's called by mod and mission makers, it's executed after settings are initialised.
• Store the people sitting on the seats, so that multiple people can sit at once. Fixes ACE Sitting only allows 1 sitter on multi-seatable objects #10486.
• Pass new ownership onto other people sitting, if existent, instead of keeping it until everyone has left the bench.

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