all: using double precision, sync thread loop exit

We're seeing double now. Only not. OpenGL is still float (which is perfectly fine). But the engine should behave a bit better. Also, threads could speed up and start moving before any other thread had completed force calculations. This wouldn't be good. I measured a slowdown of 0.20 timeunits per 10 seconds IRL. Also yes, if you have verbosity set to 8 you can see how much time has progressed in terms of simulation. As in, how much time have we simulated. Don't bring out your LorentZ transformations yet though, we're still static.