Add method to get the source of a TNTPrimed. Adds BUKKIT-3815

By: AlphaBlend <whizkid3000@hotmail.com>

paper-api/src/main/java/org/bukkit/entity/TNTPrimed.java

@@ -12,9 +12,27 @@ public interface TNTPrimed extends Explosive {
     public void setFuseTicks(int fuseTicks);
 
     /**
-     * Retrieve the number of ticks until the explosion of this TNTPrimed entity
+     * Retrieve the number of ticks until the explosion of this TNTPrimed
+     * entity
      *
      * @return the number of ticks until this TNTPrimed explodes
      */
     public int getFuseTicks();
+
+    /**
+     * Gets the source of this primed TNT. The source is the entity
+     * responsible for the creation of this primed TNT.
+     * (I.E. player ignites TNT with flint and steel.) Take note
+     * that this can be null if there is no suitable source.
+     * (created by the {@link org.bukkit.World#spawn(Location, Class)}
+     * method, for example.)
+     *
+     * The source will become null if the chunk this primed TNT is in
+     * is unloaded then reloaded. If the source Entity becomes invalidated
+     * for any reason, such being removed from the world, the returned value
+     * will be null.
+     *
+     * @return the source of this primed TNT
+     */
+    public Entity getSource();
 }