iNaturalist / Flickr deduplication - groundwork

This simply changes the is_this_image_in_flickr() function to return data about the flickr image, if it exists. The function name is also changed to image_in_flickr() to reflect this.

These changes leave the behaviour of the code completely unaltered for the moment. But it should allow future alterations which carry out a more sensible deduplication effort (see http://eol.org/forums/11/topics/28).