Added webpack.ProvidePlugin for most used imports

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

app/javascript/gabsocial/pages/group_page.js

@@ -1,5 +1,3 @@
-import React from 'react';
-import { connect } from 'react-redux';
 import { PropTypes } from 'prop-types';
 import ImmutablePropTypes from 'react-immutable-proptypes';
 import ImmutablePureComponent from 'react-immutable-pure-component';