Added webpack.ProvidePlugin for most used imports

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

app/javascript/gabsocial/features/groups/timeline/components/header.js

@@ -1,6 +1,4 @@
-import React from 'react';
 import ImmutablePropTypes from 'react-immutable-proptypes';
-import PropTypes from 'prop-types';
 import Button from 'gabsocial/components/button';
 import ImmutablePureComponent from 'react-immutable-pure-component';
 import { defineMessages, injectIntl } from 'react-intl';

app/javascript/gabsocial/features/groups/timeline/components/panel.js

@@ -1,4 +1,3 @@
-import React from 'react';
 import ImmutablePureComponent from 'react-immutable-pure-component';
 import ImmutablePropTypes from 'react-immutable-proptypes';
 import { injectIntl, defineMessages } from 'react-intl';