Room grid types

Variables
const int	Renga::GridTypes::Room::Undefined = 0
	Undefined grid.
const int	Renga::GridTypes::Room::Floor = 1
	The face considered as room floor.
const int	Renga::GridTypes::Room::Ceiling = 2
	The face considered as room ceiling.
const int	Renga::GridTypes::Room::Wall = 3
	The face considered as room wall face (side surface)