Add `harden`, `ssh`, `ufw` and `rssh`

This pull request:

- adds [alphagov/puppet-harden](http://github.com/alphagov/puppet-harden), a Puppet module to secure a base installation of Ubuntu
- adds [attachmentgenie/ssh](http://forge.puppetlabs.com/attachmentgenie/ssh), a customisasble SSH module for Puppet
- adds [attachmentgenie/ufw](http://forge.puppetlabs.com/attachmentgenie/ufw), a customisable UFW module for Puppet  
-- adds firewall rules in `ufw.pp` to restrict SSH access
- adds [blom/rssh](http://forge.puppetlabs.com/blom/rssh), a Puppetised version of rSSH  
-- adds configuration to restrict a shell to using only rsync