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__/avatar-test.js

@@ -1,4 +1,3 @@
-import React from 'react';
 import renderer from 'react-test-renderer';
 import { fromJS } from 'immutable';
 import Avatar from '../avatar';