Replace float/UInt64 durations by a more precise Time class (#388)

Improve Clock class with atomic RestartIfOver method and allows to choose required precision

include/Nazara/Core/Systems/SystemGraph.inl

@@ -32,7 +32,7 @@ namespace Nz
 	}
 
 	template<typename T>
-	void SystemGraph::Node<T>::Update(float elapsedTime)
+	void SystemGraph::Node<T>::Update(Time elapsedTime)
 	{
 		system.Update(elapsedTime);
 	}