Some improvements

First commit allows add a try block to catch the exception thrown by Bukkit when a permission was already registered, so admins can reload Residence (for example, to update it using PlugMan on a live server)

Second commits makes movement listeners optional. They're the most computationally-intensive thing packed on Residence and personally I don't let users block anybody from entering their residences, so it's a waste of CPU. They're however enabled by default, being therefore a non-breaking change.