Implement Leash API. Adds BUKKIT-4459, BUKKIT-4583

src/main/java/org/bukkit/craftbukkit/entity/CraftLeash.java

@@ -0,0 +1,27 @@
+package org.bukkit.craftbukkit.entity;
+
+import net.minecraft.server.EntityLeash;
+
+import org.bukkit.craftbukkit.CraftServer;
+import org.bukkit.entity.EntityType;
+import org.bukkit.entity.LeashHitch;
+
+public class CraftLeash extends CraftHanging implements LeashHitch {
+    public CraftLeash(CraftServer server, EntityLeash entity) {
+        super(server, entity);
+    }
+
+    @Override
+    public EntityLeash getHandle() {
+        return (EntityLeash) entity;
+    }
+
+    @Override
+    public String toString() {
+        return "CraftLeash";
+    }
+
+    public EntityType getType() {
+        return EntityType.LEASH_HITCH;
+    }
+}