Install some new services when provisioning

This PR adds some new packages and changes the way some packages are install, as follows:

* Node.js is now installed via the [Puppet Node module](https://github.com/puppetlabs/puppetlabs-nodejs), which gives a much more recent version
* Ruby and Rubygems are now installed via the [Puppet Ruby module](https://github.com/puppetlabs/puppetlabs-ruby), rather than as a byproduct of `ruby-sass`
* SASS (from Rubygems rather than `apt`), Bower and Require.js are now installed
* SQLite is now installed
* Memcached is now installed. I've allocated 10% of memory usage to Memcached, as that should be enough for development