Add images for ship explosion
Add getCenter Method to Entity class
change genAstExplosion to explosion and refactor logic explosions
Change class name for UtilituMath and UtilityGeom to MathUtil and
GeomUtil respectively, move some methods from MathUtil to GeomUtil
remove unnecessary print
Add Font load methods and add a new font: Comic Sans MS.
Now the application call System.exit when user press the back button
Move draw based on alpha  of Shield to new subclass of Picture
AlphaLifePicture.
Change logic for missile regeneration.
Add PauseUI for pause menu. Add ScreenUtil class with util methods for
center actors over others. Add images for run button. Add method in
BasicUI for create image button with or without text.
Run world method now call from showGame on GameScreen. change to if-else
struct code in world act method
Change calculation of rOrientation for Ship. Now Ship reset its
rOrientation property, so when touch both arrows it gonna be zero.