Set up monit to monitor app services

The monit dashboard is available at port 2812, or 2067 on Vagrant. It
currently only attempts to restart failed services; it doesn't send
alerts based on CPU usage, disk space, etc because it wasn't clear how
that would work for transit agencies.

The default interval for monit to perform its checks is 120 seconds (at least on Ubuntu). I'm leaning toward making that shorter, but I think it's within the bounds of reasonableness, so I've left it as-is for now.

Here's an example of what the monitoring dashboard looks like:
![monit](https://cloud.githubusercontent.com/assets/447977/4240454/f0371ef0-39ea-11e4-9494-433be84f2915.png)

I've tested this by manually killing off processes and checking to see whether monit puts them back.

Probably should move this up to where the other apt-install's are -- almost didn't find this when I was looking for it