Secret upper limit for time step when using SimWindow

[mxgrey]

It turns out that the SimWindow class secretly does not support simulation time steps which exceed 1.0/30.0. This is because of this line. The variable mDisplayTimeout is equal to 1000.0/30.0 (it gets set here) so then if mWorld->getTimeStep() is greater than 1.0/30.0, then mDisplayTimeout/(mWorld->getTimeStep()*1000) will come up as 0. This instructs the window to run 0 simulation iterations per refresh.

One option would be to change the line to

int numIter = ceil(static_cast<double>(mDisplayTimeout) / (mWorld->getTimeStep() * 1000.0));

This would guarantee that a simulation timestep is always called at least once per refresh. I think a more satisfying solution would be to just have a variable in SimWindow that lets the user determine how many simulation iterations are run per refresh.