Summary: Fixes#3679, see https://github.com/facebook/react-native/issues/3679
The idea is to always load images from the same folder that we loaded JS bundle.
This doesn't change the current behavior, since `imageNamed:` inferred the
absolute path to the image from app's bundle, but now we make it explicit.
The benefit for OTA updates implementations is that they can simply ask RN
to load js from some `~/Documents/<build-id>/main.jsbundle` folder and RN will
look for images in `~/Documents/<build-id>/assets/`.
Note that for Android we will have to come out with a different plan, since
in prod we load images from built-in resources.
public
Reviewed By: vjeux
Differential Revision: D2616995
fb-gh-sync-id: 2906c62380280ecb987525edf9a0e3e727a1008b
10b599c343