Added the scoreboard. Misc. changes.

* ScoresState.cs:
  Initial version.

* MenuState.cs, DifficultyState.cs:
  Removed static method callbacks.

* EndGameState.cs:
  Removed static method callbacks.
  Now calls ScoresState.AddScore().

* GameState.cs:
  Removed static method callbacks.
  Implemented block scoring.

* State.cs:
  Renamed a few methods that were missed when converting things from
  the Game state.
  Made input reset when the state is left.

* ButtonList.cs:
  Fixed an infinite loop when input is reset.

* Log.cs:
  Made the exception handler only print the message.