Function getShortViewerUrl

Gets a short url object for a given item url.

For example, passing https://viewer.mediafly.com/bling#/item/b2b81a466651492db55ec16d92264fd4product207989 returns an assets link like "https://assets.mediafly.com/l/ybASVXR24mW4".

This is used to power the "Create Viewer Link" feature.