front: Specify maximum screen size in config file.

This allows us to remove some AE customizations on the native side that
are blocking SDL 2.0 compatibility.
gles2rice: Simplify custom video initialization, compatible with SDL 2.

Use config file rather than SDL_GetVideoInfo to get maximum screen
size.  SDL_GetVideoInfo was removed from SDL 2.0, so this also improves
forward compatibility.