Pocket Urns

- On respawn, Pocket Urns runs after other mods return items. It no longer
hands back an urn that another mod (a grave or keep-inventory mod) already
returned.
- On respawn, it removes any copy of an urn that is already placed in the
world, and any second copy of the same urn.
- If another mod hands back an urn later (for example from a grave), it is
thrown away if the player already holds that urn.
- A dropped urn disappears when touched if the player already holds it or
it is placed in the world.
- Urns that have never been placed are never removed.