Simplify Store Boilerplate

[sleexyz]

Right now we require that a whole block of text be copy and pasted and search/replaced.

Perhaps we can try faking ML modules by having fields of classes that are themselves first-class classes that are closed over type variables.

[sleexyz]

The tricky part is partially applying type parameters to resulting classes, i.e. applying the Store type variable to an Action (A => Store => B, but leaving A and B generic.

We should just annotate actions inline then, or recommend that people put a additional type alias in their efx.js file.