Implement Comparable for generated Java classes

[joshsh]

The Hydra terms of any given type are totally ordered; you can compare any pair of terms for equality, greater than, or less than. That property extends to generated code, as well: if any pair of objects has the same logical type, and both objects have a term representation, you should be able to compare them. This is true of generated code in Haskell, but is only partially true of generated code in Java; in Java you can test two objects for equality, but you can't test them for greater than or less than. Fix this. Implement Comparable<A> for each A which currently implements Ord in Haskell.