carts:manage_attachment does not handle the driver value of the cart,
hence carts could not be used by another player until it's replaced.

Fixes #2681

Junglegrass is unchanged as a source of cotton seeds for now, but
probably should be removed as a source in future, as players get
used to the new source.

Before it was rendering the side on both the side and the front of the minetest.inventorycube

Introduce _c and _d door types to correctly render the texture faces for the open and closed state.

Previously, cloud density was too low at medium humidity.
Tune cloud density variation to match the default/classic value at
humidity midvalue 50.
Tune the lower limit of cloud density that occurs at extreme low
humidity.
Increase minimum cloud thickness to 2 nodes.
Add comments.

The player should always be teleported away when they die and
we can still fall back to the engine spawning code.

This is not directly related to player models but fits well
as a convenience feature in player_api.