Support get size info by context

Just a idea, a decorators function: (just like react-redux connect)

import React, { Component, PropTypes } from 'react';
import { getLayoutSize } from 'react-native-layout-tester';

@getLayoutSize(layout => ({
  deviceName: layout.label,
  deviceWidth: layout.width,
  deviceHeight: layout.height,
}))
class Comp extends Component {
  static propTypes = {
    deviceName: PropTypes.string,
    deviceWidth: PropTypes.number,
    deviceHeight: PropTypes.number,
  };

  render() { ... }
}

Also, we can have a default config, it can get Dimensions info and no test wrapper. It can be used for production, and keep the same code.

@machadogj what do you think?

[machadogj]

Tested the PR and works like a charm. Added a minor, updated docs and published to npm. Thanks for your help!

[machadogj]

@jhen0409 Done. Updated repo and npm!