La clase Grafico

On branch master
modified:   gen/org/example/asteroides/R.java
new file:   res/drawable/fondo.jpg
new file:   res/drawable/misil1.png
new file:   res/drawable/misil2.png
new file:   res/drawable/misil3.png
new file:   res/drawable/nave.png
new file:   res/drawable/nave_fuego.png
new file:   res/layout/juego.xml
new file:   src/org/example/asteroides/Grafico.java
new file:   src/org/example/asteroides/Juego.java