Allow the randomly generated seed to be saved so that experiments / benc...

...hmarks can be recreated in the future

Because firstSeed() and nextSeed() are not member variables, I had to add a locally global (within the .cpp file) variable to store the seed. I couldn't think of a better way to do this.

Also, is there a better style guideline for this global var? 
What if first_seed is not yet initialized?