Consider generalizing Lambda Graph's collection types

[joshsh]

Hydra's formal data model (Lambda Graph) currently includes type and term constructors for two special kinds of recursive data structures: lists and maps. Since uniqueness of keys is technically not enforced, maps can be considered as syntactic sugar for lists of pairs. Optionals are also supported.

Now that these types are fully supported in both Haskell and Java, consider generalizing them, perhaps even introducing general-purpose support for functors, applicatives, and monads. The current support for lists and maps can serve as a regression test for the more generic solution. Perhaps even Hydra's built-in Flow monad can be brought into a generalized Lambda Graph data model.

[joshsh]

Bumping. Still a good thing to consider prior to Hydra 1.0, though only after closing the loop.