Implement commandline option --set.

This is one of the first steps towards automation.
Added documentation for --set in help.txt.
Reformatted help.txt to wrap lines nicely,
in case the user's terminal doesn't already.
Add population diff to JStatusPane.
Implement commandline option --seed.
Implement commandline option --statistics.

See --help for detailed description how it works.
Internally using shutdown hooks, so NEARLY EVERY entry is written.
The only remaining problem might be the GUI terminating
WHILE main() is writing out data.
But that's not the intended use-case anyway;
see the upcoming --automate flag.
Implement commandline option --automate-for and companions.

See description in --help for usage, and what --no-gui,
--exit-after and --go-fast do.
Implement Pause and Go Fast.

Added Buttons in GUI to toggle these two settings.
Added commandline options to toggle these settings.
Added documentation for --help for these two settings.
Add keybinding for pause/unpause.
Implement and document reset button.

Also, make all parameters mutable, since we can reset the field.