Sync point in program and visualizatin scripts.

Master and slaves should add synchronization at the very beginning. Visualization script then recognizes those points and shifts log times accordingly.

The picture now is much more correct - master waits for result AFTER slave work.
Less waiting in slave start.

There was redundant receive "(DnaStarted slavePid) <- expect" in Message.hs. It basically sequenced start of compute slaves, reducing available parallelism.