Print more stats in the PingPong example

Now includes start time=the time to start the system and all actors, and a total time:

|Throughput| Messages/sec| Start system [ms]| Total time [ms]|
|---------:|------------:|-----------------:|---------------:|
|         1|      4602000|              7.53|         6525.55|
|         5|     17492000|              6.48|         1722.10|
|        10|     22590000|              6.63|         1334.78|