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();
     }
 }

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

@@ -159,9 +159,6 @@ public class SpongePlayer extends PlotPlayer {
                 return;
             case NOT_SET:
                 this.player.offer(Keys.GAME_MODE, GameModes.NOT_SET);
-                return;
-            default:
-                this.player.offer(Keys.GAME_MODE, GameModes.NOT_SET);
         }
     }
     
@@ -186,7 +183,8 @@ public class SpongePlayer extends PlotPlayer {
     public void playMusic(Location location, int id) {
         switch (id) {
             case 0:
-                this.player.playSound(null, SpongeUtil.getLocation(location).getPosition(), 1);
+                //Placeholder because Sponge doesn't have a stopSound() implemented yet.
+                this.player.playSound(SoundTypes.BLOCK_CLOTH_PLACE, SpongeUtil.getLocation(location).getPosition(), 0);
                 break;
             case 2256:
                 this.player.playSound(SoundTypes.RECORD_11, SpongeUtil.getLocation(location).getPosition(), 1);