User activity timestamps

Addresses the back end of #722.

Requires database update 00722_player_activity_01.sql, followed by a regeneration of the views in views.game.sql and views.player.sql.

Note that already-existent games and players receive a timestamp of zero. If it is necessary to replace game timestamps of zero, this can be done at a later time.

http://jenkins.buttonweavers.com:8080/job/buttonmen-blackshadowshade/206/