After the system is added to the engine, this method is called every frame until the system
is removed from the engine. Override this method to add your own functionality.
<p>If you need to perform an action outside of the update loop (e.g. you need to change the
systems in the engine and you don't want to do it while they're updating) add a listener to
the engine's updateComplete signal to be notified when the update loop completes.</p>
@param time The duration, in seconds, of the frame.
After the system is added to the engine, this method is called every frame until the system is removed from the engine. Override this method to add your own functionality.
<p>If you need to perform an action outside of the update loop (e.g. you need to change the systems in the engine and you don't want to do it while they're updating) add a listener to the engine's updateComplete signal to be notified when the update loop completes.</p>
@param time The duration, in seconds, of the frame.