Added webpack.ProvidePlugin for most used imports

Removed imports of React, connect, PropTypes throughout
Removed the "React" in React.Component/PureComponent

app/javascript/gabsocial/components/__tests__/button-test.js

@@ -1,5 +1,4 @@
 import { shallow } from 'enzyme';
-import React from 'react';
 import renderer from 'react-test-renderer';
 import Button from '../button';