Added a horse rental function to the stable.

This function allows you to either rent a horse, or rent out your own horse.

For a fee of 100,000 Silver you can rent a horse for seven days. The owner of the horse may forcefully retrieve their horse when the rented horse is checked into a stable, or if you are not connected to the game.

You can enjoy the effects of the gear already equipped on the rented horse, but you will not be able to unequip any gear from the rented horse.

You can rent out up to Tier 8 horses.