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.
Fixed stack acciddent bug in PlayerOptions lua functions.  Added skew and tilt mods to PlayerOptions::GetMods and FromOneModString for when the perspective isn't one of the old ones.
Made PlayerState:GetCurrentPlayerOptions safe to use.  Added Docs/Themerdocs/modslevel.txt to explain what ModsLevel should be used by a theme using the new PlayerOptions interface.
Merge pull request #149 from sigatrev/NoteField-Board

Allow NoteField Board to be an AutoActor
Merge pull request #150 from kyzentun/player_options_fix

Fixed stack acciddent bug in PlayerOptions lua functions.