Added showing/dismissing completed games

Added was_game_dismissed to SQL, modified BMInterface->get_all_games()
to filter on it, updated Overview.js to display completed games (again)
based on it, added a link to dismiss those games, and implemented
responder/Interface methods to set was_game_dismissed when it's clicked.
Improved clarity and consistency

In comments, SQL syntax, and user messages.
Merge pull request #1031 from AdmiralJota/604_dismiss_completed_games

Display and dismiss completed games on Overview