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/generic_not_found/index.js

@@ -1,4 +1,3 @@
-import React from 'react';
 import Column from '../ui/components/column';
 import MissingIndicator from '../../components/missing_indicator';