Changes to get Frodo working on Heroku

Hi Folcon - I've made a few changes to the repo to get it working on Heroku - could you let me know whether this works?

I've commented the reasons for the changes in the individual commits - maybe this PR is a better place to talk about how Nomad/Frodo work together to start the webserver?

You should be able to test this in dev mode with just `lein dev`, or prod mode with `NOMAD_ENV=prod PORT=<port> lein prod`

Let me know if you've got any questions!

James