Retrieve multiple images

Until ias retrieved just one image at a time, that request could be made asynchronously.

Now more than one image can be possibly retrieved and ias has to make a "sharing http request" for each of them. From the client point of view, the above requests should be atomic, the client just wants a list of already shared images.

The solution was making "sharing requests" synchronously and sequentially, so at the end of the for loop either ias has a list of shared images or it raises an error.