FIXED Problems with permissions for save games on Android.
FIXED Crash when resuming game from saved state when viewing a design.
FIXED Call SDL_DestroyRenderer and SDL_DestroyWindow, rather than just
relying on SDL_Quit (problems on AmigaOS and AROS with SDL 2).
UPDATED If playing with nukes disabled, more sectors can now instead build
spaceships.
UPDATED On Android, show a toast to say if save game is successful or not.
UPDATED Now compiled with SDL 2.0.8, SDL_image 2.0.3, SDL_mixer 2.0.2 on
Windows and Android.
UPDATED Now targetting Android 8.1.