RFC: ES6 container

[RFC document](https://github.com/MajorBreakfast/rfcs/blob/master/active/0000-es6-container.md)
Things I don't like about the current container:
- colon obsessiveness: `api-adapter:main`, `store:main` just because we need a colon
- hides module system
- `container.lookup('type:name')`, do I get a singleton or a new instance? Can't tell