.meta module binder update

This PR changes `.meta` module from containing a single blueprint for the eponymous export of a module, to containing a `module-binder`, a binder for a module containing a blueprint for each export.

The .meta files in the Montage were updated using this script at https://gist.github.com/Stuk/1ec8d466b3f792ed53b7 . We should hold off updating .meta files in other projects until further changes using the `ModuleReference` from #1225 have been made.

These are the javascript files that have changed:

* core/core.js https://github.com/montagejs/montage/pull/1230/files#diff-10
* core/meta/binder.js https://github.com/montagejs/montage/pull/1230/files#diff-14
* core/meta/blueprint-reference.js https://github.com/montagejs/montage/pull/1230/files#diff-16
* core/meta/blueprint.js https://github.com/montagejs/montage/pull/1230/files#diff-18
* core/meta/module-binder.js https://github.com/montagejs/montage/pull/1230/files#diff-22
* + spec/test files