Reorganize fixture compilation; minor improvements.

Compile only .json files, rename fixture compiler to allow for other postinstall
steps, add `moment` to the module's dependency list (we're going to need it
inside of the library eventually, so it's not a test-only dependency), and move
the fixtures.js output file in to fixtures/compiled.js so it's clear that the
file is automatically-generated and isn't a unit test.