Files should always end with new lines to avoid introducing extraneous diffs.

This introduces preliminary support for 1. retrieving photo metadata for a place and 2. persisting the associated photos to disk where they can be accessed via react-native using an `<Image>` tag.

Example usage via JS:

```javascript
const placePhotos = await RNGooglePlaces.getPlacePhotos(placeId)
const firstPhotoUri = await RNGooglePlaces.getPlacePhoto(placePhotos[0])

console.info(firstPhotoUri)
```

Place photos shouldn't be persisted indefinitely. We write them to a cache directory so that the OS knows that it can clean these files up if necessary.

This also removes specifying context.MODE_PRIVATE when creating the FileOutputStream, which doesn't seem necessary.

This makes the return type consistent with the method's current naming.

File.toURI returns a URI, not a Uri.

ResultCallbacks (vs ResultCallback) allows us to factor out status checks because we can define specific handlers for success/failure cases.

ResultTransform allows us to neatly chain API calls without needing to pass promise references down deeply into multiple methods.

I'd believed that this wasn't required when using .then(...).andFinally(...) pattern, but according to the console warnings this was resulting in, it is indeed required.