add game_state class, separate from play_controller
move game_state to its own file
remove unused member (dead code)
tweaks to play_controller::init

moved game_events manager init earlier
moved place_sides_in_preferred_locations to game_state
move some initializing from play_controller to game_state
add game_state::to_config
Merge branch 'master' of git://github.com/wesnoth/wesnoth