Extend Clock class

[rgrieder]

The Clock? class is used to precisely measure time by means of the operation system internal timer. When GameStates are ticked, they get a reference to a Clock object. But this may not be the only usage. Every Level needs to have a Clock that can be paused and resumed.
That implies some changes in Clock: You have to be able to tick it from outside. I therefore suggest putting the current contents of Clock to a new RealTimeClock (or a suitable name) class and rewriting Clock so that it gets ticked with a RealTimeClock object (which supports getDeltaTime()).
Feel free to examine the Clock class and its usage and then decide what is the best concept for us. The text above is only a suggestion. But clearly, this topic has to be dealt with soon.

[rgrieder]

Revised: Use the Scene class to accumulate time. This would require reorganising it a bit to tick it's content (instead of GSRoot). The clock class should stay.

Since the ticket then seems almost insignificant, I close it.