Fix Basic Auth for new version of Express

Express 4.x no longer supports Basic Auth in middleware. 

Hence, use the node-basicauth package instead. This requires 
CoffeeScript but so do some of our other packages, so there are
no new major dependencies. 

We use Basic Auth to password-protect our sites on Heroku if required.

You can test this by setting BASIC_AUTH_USER and BASIC_AUTH_PASS
environment variables.