Various scoreboard improvements. (#2204)

- Correctly remove objectives that use heart type.
- Also sends remove score packets on server switch.
- Players are only removed if Team packet mode is 4.

api/src/main/java/net/md_5/bungee/api/score/Objective.java

@@ -22,5 +22,5 @@ public class Objective
     /**
      * Type; integer or hearts
      */
-    private final String type;
+    private String type;
 }