[example] finetuning CaffeNet on Flickr Style data

This example shows how to fine-tune the BVLC-distributed CaffeNet model on a different dataset: [Flickr Style](http://sergeykarayev.com/files/1311.3715v3.pdf), which has style category labels.
The dataset is distributed as a list of URLs with corresponding labels.
Using a script, we will download a small subset of the data, split it into train and val portinos, and use the ImageDataLayer to load images directly from the filesystem.
Oh, I only just saw this -- I would have replied here. I'm not comfortable with filing snapshots as "data" as they are models, merely intermediate ones on the way to the "final" model, which is only chosen by accepting a given validation error in most cases.