add SingletonBehaviour class for managers, etc

Assets/Scripts/Util.meta

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Assets/Scripts/Util/SingletonBehaviour.cs

+using UnityEngine;
+using System.Collections;
+using System.Collections.Generic;
+
+// singleton behaviour
+// if your script will have a single instance that needs to be accessed by other scripts,
+// it should subclass SingletonBehaviour
+// primarily used for Manager scripts
+public abstract class SingletonBehaviour<T> : MonoBehaviour where T : SingletonBehaviour<T> {
+
+	private static T _instance;
+	public static T instance {
+		get {
+			if (_instance == null) {
+				_instance = Object.FindObjectOfType<T>();
+				if (_instance == null) {
+					Debug.LogErrorFormat("Missing instance of {0} in scene.", typeof(T).Name);
+				}
+			}
+			return _instance;
+		}
+	}
+}

Assets/Scripts/Util/SingletonBehaviour.cs.meta

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