Add support for goog.module (Closure) based imports

- option to enable Closure modules
- golden file based tests
- based on moduleName for the current file
- fails for export *

Based on @vojtajina's initial work.
John: could you PTAL? I think I fixed all remaining issues, including the
transform part.

Erik Arvidsson <notifications@github.com> schrieb am Thu Dec 04 2014 at
12:37:10:

> In test/closure/BasicImport-expected.txt:
>
> > @@ -0,0 +1,4 @@
> > +goog.module("test/closure/BasicImport.js");
> > +var Foo = goog.require("./deps/foo").Foo;
> > +console.log(Foo);
> > +//# sourceURL=test/closure/BasicImport.js
>
> Don't worry about it.
>
> —
> Reply to this email directly or view it on GitHub
> <https://github.com/google/traceur-compiler/pull/1559/files#r21333891>.
>