Created variable, reference for LayerMask

* Created LayerMaskVariable and LayerMaskReference. This type is often used to filter objects for collision detection to specific layers specified in the Flag value.

Assets/SO Architecture/References/LayerMaskReference.cs

@@ -0,0 +1,11 @@
+using UnityEngine;
+
+namespace ScriptableObjectArchitecture
+{
+	[System.Serializable]
+	public sealed class LayerMaskReference : BaseReference<LayerMask, LayerMaskVariable>
+	{
+	    public LayerMaskReference() : base() { }
+	    public LayerMaskReference(LayerMask value) : base(value) { }
+	}
+}

Assets/SO Architecture/Variables/LayerMaskVariable.cs

@@ -0,0 +1,12 @@
+using UnityEngine;
+
+namespace ScriptableObjectArchitecture
+{
+	[CreateAssetMenu(
+	    fileName = "LayerMaskVariable.asset",
+	    menuName = SOArchitecture_Utility.ADVANCED_VARIABLE_SUBMENU + "LayerMask",
+	    order = 120)]
+	public class LayerMaskVariable : BaseVariable<LayerMask>
+	{
+	}
+}