move the ssh PasswordAuthentication check to after installing ssh

instead of installing roundcube from Ubuntu (before replacing it), just install the dependencies we need

I had previously awkwardly disabled it because on my VPS the necessary kernel
module wasn't available. I meant to make it an option, but instead I took
out the apt-get install. Now it works for me so I'm putting everything back.

Force the scripts to run in bash

nsd doesn't install without creating the `nsd` user first - merge branch from randallsquared-master, fixes #25

fixes #23

Fix install of php5-cgi, roundcube SQL directory on Ubuntu 14.04

Not sure if I've tested this. Also because of graylisting there's not much of a need
to do sophisticated spam filtering, at least based on the email I get.

DNS test: also check a public nameserver to verify that the registrar (or up-host) configuration is correct too

remove apache before installing nginx --- it's not needed and will start complaining about the port being in use, or it might interfere with nginx

When I re-did this, I left in an old reference to the php-fcgid
script that never made it into the repo. Deleting that and moving
the php-fcgid configuration on top of it.

fixes #9
see 2ebd9706

remove old Amazon EC2-related things since no one should ever deploy a mail server to EC2 (IPs have bad reputation)

update how we get the missing roundcube SQL directory: not sure previous URL was correct, should also match the deb version