[ES6] Use module everywhere

[oliviertassinari]

Fix #2558.

[newoga]

If we can get the babel 6 in with the state 1 preset, we can use the export extensions to simplifiy this.

All of them can be like:

export  {AppBar} from './app-bar';

[oliviertassinari]

That's good to know.

[joehua87]

Hello, I see that 1 line export is not considered a good practice. https://github.com/airbnb/javascript#10.3

[alitaheri]

They are bad for files that perform logic, true. but for files that the only thing they do is re-export i think it makes sense. without this syntax the number of lines become excessively large and hard to maintain.

[alitaheri]

@newoga Yeah, but babel 6 proved too difficult apparently, for now this is good enough.

[alitaheri]

Thanks 🎉 👍