Game-based fixes

   * There's a new game retrieval function which replaces most of the other game retrieval functions on the site.
   * I renamed `nearest_game` to `imminent_game` because "imminent" is less chronologically vague than "nearest"
   * Breakout bar now displays the human/zombie status of the last game to have started.
   * Meal ticker now only gets meals from the most recent game.
   * My decorators and validators no longer break the site if no games have been defined, or if the user is not a player this game.

This addresses issues #122, #123, and #124.