support story as HTML Node

[nogizhopaboroda]

example:

import { storiesOf } from 'modulor-storybook';

const $el = document.createElement('my-component');

storiesOf('My component')
  .add('default', () => $el);

This is needed to render react, vue, etc components and templates rendered by hyperhtml, bel, yoyo, etc

[pankajpatel]

this one is completed in #48. Closing!

[nogizhopaboroda]

wait, that merge request was not merged