New GenericSingleton

using UnityEngine;
using System.Collections;

public class Singleton<T> : MonoBehaviour where T : Component {
    [SerializeField]
    bool _persistent = false;

    private static T _instance;
    public static bool IsInstantianted { get { return _instance != null; } }

    public static T Instance {
        get {
            if (_instance == null) {
                _instance = (T)FindObjectOfType(typeof(T));
                if (_instance == null) {
                    Debug.Log ("Instance: _Loading");
                    Application.LoadLevelAdditive("_Loading");
                    _instance = (T)FindObjectOfType(typeof(T));
                }
            }
            return _instance;
        }
    }

    public virtual void Awake() {
        if (_persistent)
            DontDestroyOnLoad(this);
        if (IsInstantianted) {
            Debug.LogWarning("Only one " + typeof(T) + " is allowed, destroying " + gameObject.name + ".");
            Destroy(gameObject);
        } else {
            Debug.Log ("Awake: _Loading");
            Application.LoadLevelAdditive("_Loading");
            _instance = (T)FindObjectOfType(typeof(T));
        }
    }
}