Changes

Add support for Horse inventories (#2558)

* Can now open horse inventory

Command still needs testing and needs to be updated to use `autoExecute`

* Update command to use `autoExecute`

* Move errors and fix slot default value

* Change order of types

`public static` sounds better than `static public` in my opinion

* Fix `expire:` argument throwing an error when it shouldn't

* Cast to `CraftAbstractHorse` and throw exception to prevent NPE

* Update error messages
 (commit: 74f28ba)