Replace unnecessarily expensive methods

[Aurelien30000]

Replace some methods retrieving heavy and unused data, such as:

• Since a getter exists to load and return the chunk of specific IOwnedLand, we should simply return a Set<IOwnedLand> instead of a Map<Chunk, IOwnedLand>.

public interface IWorldGuardManager {
    ...
    Map<Chunk, IOwnedLand> getNearbyLands(Location loc, int offsetX, int offsetZ);

• Avoid as much as possible working with Bukkit chunks.