gradle: Set compatibility configuration to Java 7
ClockObserver: Removed unused Clock parameter from tick() method
Clock: Removed unused fields and methods
GliderShape: Removed unused class

... and renamed GliderShape2 to GliderShape instead
Clock: Removed unused startTick field
ModelViewer: Merged trivial createModelCanvas() method into init()
XCGame: Split ModelViewer from XCGame class
Removed unused class ModelViewer
FlyingDot: Simplified makeTurn() method
ModelCanvas: Removed width and height fields

Use getWidth()/getHeight() instead
Hill: Replaced int-based orientation field by enum
GliderUser: Use UP for faster, DOWN for slower

Instead of UP for toggling
Landscape: Simplified myHill() and renamed to getHillAt()
Landscape: Simplified getHeight() method
Landscape: Simplified removeTile() and nextHill() methods