Basic implementation of turn-based logic between JQuery/Ajax and routes.

Changed session[:user_id] to session[:player_id]. player_id is more appropriate to track because Player is connected to Game.

Cookie tracks enemy_id for easier lookups. Saves us from having to do player.game.players.find { not_player } every time we need to look up the opponent.

Wrote helpers for setting up cookie enemy_id and game_id. Helpers are called in my hacky/testy start_game methods.

Wrote helper for parsing Ajax messages sent to server when a player shoots.
Wrote helper for evaluating if shot is hit/miss.
Wrote method in Player model for logging shot/results as a Guess.

Wrote helper for checking if enemy has made a new guess yet.
Wrote helper for fetching new guess.
Wrote helper for updating last_enemy_guess upon fetching new guess.
Return enemy/guess result via JSON.

Need to implement visual acknowledgement/logging of enemy guess.
Probably need to render defensive board for this purpose.

Have implemented JS logic to turn off offense board click handlers when not player's turn.
Have implemented JS logic to check/wait for opponent shot, change turn when shot received.