Provide an option to show elo deltas on the game info page.

Provide an option to show elo deltas on the game info page.

I was tired of looking at the actual elo deltas by bouncing
between the player_info and game_info pages for several
players just to see their collective elo delta values. This
provides a query parameter "show_elo" to the game info page
to show the extra elo delta column.

As a bonus, the up/down/neutral arrows on the player_info
page will take you to a scoreboard page where those values
are shown.