Quality Of Life: Export the p PropType

[nemosupremo]

This is small quality of life change that I found helpful when defining our components PropTypes. It adds the p prop type's shape and exports it. This lets you do the following for your components, instead of copying the shape:

import React, { Component, PropTypes } from 'react';
import { setLanguage, getP, PropType as p } from 'redux-polyglot';

class App extends Component {
  render() { /* ... */ }
}

App.propTypes = {
  children: PropTypes.node,
  p
};

[guillaumearm]

Hi, thanks for contributing 👍

as you explained in #73, can you add the tt translation morph ?

[nemosupremo]

Done.