Bit of clean up in the Timer template and a new function.

Timer<ClockType>::hasBeen() now *returns* how much time has gone by as a
duration type provided by the template argument.
The game loop is now framerate-independent.
I prefer these two statements together!
Paddle physics are no longer broken.
There is a new non-standard function LocalServer::createBall.

It will help the gamestate spawn a ball until a better solution is put
in place.