Added the video dataset from Franzius et al. 2008

This is a loader for the dataset from Franzius, Wilbert, and Wiskott, 2008, "Invariant object recognition with slow feature analysis".
```
      @incollection{franzius2008invariant,
        title={Invariant object recognition with slow feature analysis},
        author={Franzius, Mathias and Wilbert, Niko and Wiskott, Laurenz},
        booktitle={Artificial Neural Networks-ICANN 2008},
        pages={961--970},
        year={2008},
        publisher={Springer}
    }
```

This is definitely not the cleanest code, but I'm sending a PR per Fred's request so we can at least begin discussion about adding this dataset.