Added requestAuthorization func to objc and js file

[rangav]

This is useful to check authorization - if access granted then we can get the photos immediately without refresh of the view. currently not possible.

example usage:

GalleryManager.requestAuthorization().then(status => {
            console.log(status);
            if (status.isAuthorized) {
                // get photos
                GalleryManager.getAssets({
                type: 'all',
                limit: 10,
                startFrom: 0
              })
                 .then(r => {
                    console.log(r)
             }
       }
}