Added support for CustomModelData

src/main/kotlin/net/axay/kspigot/items/CustomItemIdentifier.kt

@@ -0,0 +1,42 @@
+package net.axay.kspigot.items
+
+import org.bukkit.Material
+import org.bukkit.inventory.ItemStack
+import org.bukkit.inventory.meta.ItemMeta
+
+/**
+ * This class defines a material in combination
+ * with a specific custom model data value.
+ *
+ * It is useful if you work with custom items
+ * defined in resourcepacks, where you do not
+ * only need a material to define a specific item
+ * type, but the value of the custom model data
+ * aswell.
+ */
+data class CustomItemIdentifier(val customModelData: Int, val placeHolderMaterial: Material) {
+
+    constructor(itemStack: ItemStack) :
+        this(
+            kotlin.run {
+                val itemMeta = itemStack.itemMeta
+                if (itemMeta != null && itemMeta.hasCustomModelData()) {
+                    return@run itemMeta.customModelData
+                }
+                return@run 0
+            },
+            itemStack.type
+        )
+
+    val itemStack: ItemStack?
+        get() {
+            val itemStack = ItemStack(placeHolderMaterial, 1)
+            val itemMeta: ItemMeta? = itemStack.itemMeta
+            return if (itemMeta != null) {
+                itemMeta.setCustomModelData(customModelData)
+                itemStack.itemMeta = itemMeta
+                itemStack
+            } else null
+        }
+
+}