Fix SSL cert and key permissions

It is bad practice to use 644 on a private key so we
have migrated the key mode to 0400. The cert is already
avaliable publicly through nginx so we have allowed it
0444.

Nothing should need to write either the cert of the key
after puppet has run, so we have denied any writing.
Give key's group permission to read
Use correct port for www rewrite
Weird invalid characters in this comment.
Refactor to use puppetlabs-apt.

This is just the first step of fixing up the repo stuff and allowing
the module to take in a package_name, but this helps replace the
execs{} with puppetlabs-apt.

Tested on:  Debian 7, Ubuntu 12.04.
Merge pull request #139 from OmarzT/master

make proxy_buffers, proxy_buffer_size, client_max_body_size configurable
Merge pull request #134 from apenney/apt

Switch to using puppetlabs-apt
Merge pull request #128 from leoc/fix-www-rewrite-port

Use correct port for www rewrite
Merge pull request #119 from alphagov/fix-permissions

Fix SSL cert and key permissions