singleton script update

[unitycoder]

@EmpireWorld can you check if this is better, then can replace with it?

// current
https://github.com/UnityCommunity/UnityLibrary/blob/master/Assets/Scripts/Utilities/Singleton.cs

// better?
https://gist.github.com/lordlycastle/64821426eedf222e66218f70e2498757

[hasanbayatme]

It is almost better @unitycoder, maybe we just needs to add the missing features from that singleton, instead of replacing it fully.