dashboard: change how wins are determined

wins are now only games where you won and at a least one other player
did not win
login: fall-back in case the session's "post_login_url" is not set
tournament form: confirm clicks on the delete button
calculate and store W_points and P_points
dashboard: report total points earned
ratings: fix bug that caused weight for multi-player games to be wrong
scorecard: add a ratings chart (powered by Google Charts)
scorecard: for each game, show effect on rating (good,bad,neutral,etc.)