Automatically reprocess stats/ratings nodes when game outcomes change

[mwiens91]

When the outcome of a game is changed (or the game is removed) currently you need to "manually" reprocess all stats and rating nodes.

This can instead be done automatically with hooks on the Game model that check if a game's outcome was changed or the game was deleted, and, if so, reprocess all stats nodes and nodes for rating periods that this change would affect.