get rid of JV (View refactor)

I want to get rid of JV, but preserve the symbolic splitting properties of View (that is, don't break everything into a scalar.

Maybe a function like

``` haskell
split :: J (f :. g) a -> f (J g a)
```

would accomplish this.

The open question is how to handle products. A little template haskell could give special lenses, perhaps
