Summary:
Image source uri's prefixed with ~ are expanded into a full path to
the app directory.
For example: `~/Documents/foo.png` is expanded into `Users/arbesfeld/Library/Developer/CoreSimulator/Devices/977988DF-A8BC-4CE5-A27A-75807A6DF085/data/Containers/Data/Application/CBEFC261-5900-4EF9-8646-603BC57B094A/Documents/foo.png`.
This lets us store and use images from the application home directory with the `Image` component:
```
<Image source={{uri: '~/Documents/foo.png', width: 300, height: 300}} />
```
Resolves#1178
Closes https://github.com/facebook/react-native/pull/1740
Github Author: Matthew Arbesfeld <arbesfeld@gmail.com>
23909cd6f6