Missing `unlock_items` on some unlock endpoints

[queicherius]

Current Behavior

The following endpoints are missing unlock_items or unlock_item:

• https://api.guildwars2.com/v2/nodes?ids=all&v=latest
• https://api.guildwars2.com/v2/mounts/skins?ids=all&v=latest
• https://api.guildwars2.com/v2/skiffs?ids=all&v=latest

Expected Behavior

All unlocks that come from items should point to their respective unlock items in some way.

Steps To Reproduce

1. Open the respective endpoint and observe missing item link.

Happening since

Jun 14, 2017

Anything else?

• https://github.com/arenanet/api-cdi/issues/543
• https://github.com/arenanet/api-cdi/issues/644