Fixed "neigh" command and made more user friendly

- Fixed "neigh" command
Neigh command returned false, so players were told it wasn't a known command.

- Made more user friendly
If you use /horse spawn while you have a horse spawned, it now acts as the call command instead of telling
the player to use /horse call, and if you use /horse call if you don't have a horse spawned, it now acts as
the spawn command instead of telling the player to use /horse spawn