Add ItemMeta factory and interfaces. This adds BUKKIT-15

Included with ItemMeta is a new serializable class Color.

PotionEffects are now serializable.

By: Wesley Wolfe <weswolf@aol.com>

paper-api/src/main/java/org/bukkit/Bukkit.java

@@ -26,6 +26,7 @@ import org.bukkit.plugin.messaging.Messenger;
 import org.bukkit.scheduler.BukkitScheduler;
 
 import com.avaje.ebean.config.ServerConfig;
+import org.bukkit.inventory.ItemFactory;
 
 /**
  * Represents the Bukkit core, for version and Server singleton handling
@@ -390,4 +391,8 @@ public final class Bukkit {
     public static WarningState getWarningState() {
         return server.getWarningState();
     }
+
+    public static ItemFactory getItemFactory() {
+        return server.getItemFactory();
+    }
 }