Update Capfile

Add tasks to update the Apache config and restart the web server.
Update ServerName in Apache config

I'll change this back when we're ready to make the switch to the new server.
Use PassengerUser instead of PassengerDefaultUser

We want to start the Passenger process as freerange so that it can
access the environment variables set within that user's shell.

I'm not sure why we were previously setting `PassengerDefaultUser` but
it doesn't appear to do what we need.
Remove SMTP_PASSWORD from Apache config

We can set this as an environment variable in the freerange user's
profile (by using `cap env:edit`) rather than having to store it in the
Apache config.