Various Sponge changes

- many improvements
- inventory utilities broke when updating to Sponge API 6.0.0

Sponge/src/main/java/com/plotsquared/sponge/object/SpongeOfflinePlayer.java

@@ -1,24 +1,30 @@
 package com.plotsquared.sponge.object;
 
 import com.intellectualcrafters.plot.object.OfflinePlotPlayer;
+import org.spongepowered.api.entity.living.player.User;
 
 import java.util.UUID;
 
 public class SpongeOfflinePlayer implements OfflinePlotPlayer {
 
+    private User user;
+
+    public SpongeOfflinePlayer(User user) {
+        this.user = user;
+    }
     @Override public UUID getUUID() {
-        return null;
+        return user.getUniqueId();
     }
 
     @Override public long getLastPlayed() {
-        return 0;
+        return 0; //todo
     }
 
     @Override public boolean isOnline() {
-        return false;
+        return user.isOnline();
     }
 
     @Override public String getName() {
-        return null;
+        return user.getName();
     }
 }