Adding maniple organ category.

[MistakeNot4892]

Description of changes

• Adds a maniple organ category for retrieving 'hand' limbs similarly to 'stance' limbs.
• Replaces hardcoded organ list in wheelchair movement code with maniple category.
• Adds an overlooked case for human post-move proc.
• Unifies wheelchair spawn checking under cannot_stand().

Dependency for octopus port.

Why and what will this PR improve

• Ease of retrieving arbitrary organ lists from species.
• More complete calling of post-move hooks.

Authorship

Myself.

Changelog

Nothing player-facing.