Way too much stuff for just one commit.
Refactored OffenseBoard and DefenseBoard to single methods, render_offense_board and render_defense_board.

Cleared up confusion in render_offense_board and render_defense_board relating to coord values between
server and client.

Modified render_defense_board to display short ship name instead of just changing color to denote a ship.

Modified player#defense_board and player#offense_board to return data structures more useful for the JS end.

Refactored helper #my_turn? to look at last guess, rather than game.current_player attribute.

Wrote 'check_game_over' controller, plus logic in JS Game object to handle checking at the end of every turn.

Added validation to prevent a player from guessing the same coord twice.

Added check to '/shoot' controller to return 'false' immediately if coord already shot.

Modified click listeners in OffenseTurn to deactivate spots already hit.

Refactored #end_turn logic in OffenseTurn.

DefenseTurn could still use a little refactoring.