Expose decorate to plugins

[timneutkens]

This adds the ability to require('hyper/decorate') to register your own decorators from plugins 🌟
Will allow plugins to create a React component that can be extended by other plugins.

Example:

import React, {Component} from 'react'
import decorate from 'hyper/decorate'

class MyComponent extends Component {
  render () {
    return (<div>My Component</div>)
  }
}

export default decorate(MyComponent, 'MyComponent')

Then in plugin code:

import React, {Component} from 'react'
export function decorateMyComponent (MyComponent) {
  return class extends Component {
    render () {
      return (
        <div>
          <MyComponent {...this.props}>
          <div>Something else</div>
        </div>
      )
    }
  }
}

[albinekb]

Awesome! Super neat 😎