some refactors + better id setting

src/main/java/net/hexa/MythicItems/Mythics/MythicItem.java

@@ -0,0 +1,28 @@
+package net.hexa.MythicItems.Mythics;
+
+import org.bukkit.inventory.ItemStack;
+import org.bukkit.persistence.PersistentDataContainer;
+import org.bukkit.persistence.PersistentDataType;
+
+public abstract class MythicItem {
+    public ItemStack item;
+
+    public MythicItem() {}
+
+    public static int getMythicId(ItemStack item) {
+        PersistentDataContainer itemData = item.getItemMeta().getPersistentDataContainer();
+
+        return itemData.get(Constants.mythic_key, PersistentDataType.INTEGER);
+    }
+
+    public static boolean isMythic(ItemStack item) {
+        PersistentDataContainer itemData = item.getItemMeta().getPersistentDataContainer();
+
+        return itemData.has(Constants.mythic_key);
+    }
+
+    protected void setMythicId(int id) {
+        PersistentDataContainer itemData = item.getItemMeta().getPersistentDataContainer();
+        itemData.set(Constants.mythic_key, PersistentDataType.INTEGER, id);
+    }
+}