Implement horse mounting whitelist

[Nevakanezah]

Players who dedicate significant time towards breeding ideal horses would likely find it very valuable to control who is able to ride one of their horses. A whitelist/blacklist implementation would be most effective here, allowing players granular control over the use of their horses.

A prospective implementation of this feature should consider:

• "Training" is required to activate white/blacklist behaviour, and may have a material cost
• Only a horse's tamer should be able to modify the white/blacklist
• Options for "Allow any", and "Only me"
• White/blacklists controlled via commands using HorseID
• Players with specific permission can ignore whitelist
• Attempting to ride a horse you aren't allowed to results in dismounting, possibly minor damage.
  • Appropriate horse audio
  • Message informing the player: "That horse will only let ride it!" or similar, so people know who to talk to for access.
• Horse owner can transfer ownership via commands
  • This may need to check that the new owner is online
• An option for players to set global whitelist/blacklists that apply to every horse they own
  • Consider whether this should allow using permission nodes in the command