es6 import returns empty object

[jzimmek]

the import of Propeller returns an empty object instead of a constructor function.

import Propeller from "Propeller/src/propeller"

luckily i can workaround it by directly accessing "window.Propeller" after the import statement, but it would be better to export the correct constructor function.

i use es6 import through webpack/babel.

[PixelsCommander]

Hi . Could you introduce a PR addressing this?