Allow NoteField Board to be an AutoActor

NoteField board was already an AutoActor, but code was requiring it to
be a derivative of Sprite. Allow any ActorClass to be used.

NoteField could already be accessed from below, using GetParent() on the
NoteField Board. For ease of allowing the board to be used for player
specific purposes, make notefield an actual child of Player, so the
Board can be accessed per player from the top down.
Merge pull request #149 from sigatrev/NoteField-Board

Allow NoteField Board to be an AutoActor