shoot: specialize scene to add witdth and height

Signed-off-by: Jean Privat <jean@pryen.org>
shoot: add scene to sprites and use it to gather global width and height

Signed-off-by: Jean Privat <jean@pryen.org>
shoot: use a scale factor to compute the game dimentions

Signed-off-by: Jean Privat <jean@pryen.org>
tests: add sav/shoot_android.res

Signed-off-by: Jean Privat <jean@pryen.org>