This class exists to contain other classes neatly and to make sure that the top objects in the class hierarchy get acquainted.

The connections formed in the Tetris class are essential to the workings of the program: they determine how subsequent lower classes will interact.

They also disperse the program's flow of control:
more connections produce more dialogue between objects.

contains: Board
contains: PieceAnimator
contains: KeyInteractors
contains: PieceFactory