Initial stab at the screen object structure.  Parts include:
ScreenObj
GraphicsObj : ScreenObj
ImageObj : ScreenObj
SpriteObj : ImageObj
Point
Rectangle
AnimationDescription

Point & Rectangle are two helper classes that should be much lighter
weight than the standard models available from awt, javafx, or other
java packages.

AnimationDescription describes a set of "frames" within a spritesheet.

These require Wendi to implement the rendering routines.