remove unnecessary arguments

All of before_human_turn, play_side, play_turn had an argument
"bool save". The only use of this was by the playsingle controller
to determine whether or not to save an autosave -- it was controlled
in a single place by a single for loop in play_scenario.

Instead of polluting all of these functions, including play_controller,
and replay_controller, with arguments that they ignore, save was
replaced with a member variable of playsingle_controller. This is a
strict refactor in terms of behavior.