Remove dependency on Dokku

[jschementi]

Currently, Dokku is used to deploy the application (using Git and Heroku buildpacks) and run/serve the application (using Docker and Nginx).

However, Dokku is meant to host multiple domains on one server, so it uses Nginx to route requests to the corresponding application. For Riker's purposes, Nginx isn't required as Riker only runs one application per machine.

Riker should just use Heroku buildpacks and Docker directly.

To deploy the application, Dokku uses git, but it can also be accomplished using tar.gz+scp or rsync. Still leaning towards git though.

NOTE: For a previous project I wrote a dev environment for Docker and Vagrant, and much of that can be reused for this. Also, it's be great to use riker to run apps local as well...