Add support for GHCJS

This provides a (AFAICT) fully working GHCJS package set.

@peti Can I get your feedback on how to best merge this in? I'm sure there are some things to consider, like if/how we should specify that a given package supports GHCJS (or more generically, any particular compiler).
I don't recall.  However, since ghcjs has been updated pretty dramatically, it might be best to regenerate this entire list.  The purpose is to make sure that the entire set of built-in packages that comes with ghcjs is set to null in haskellPackages_ghcjs.