Adding a Discourse template

[Discourse](http://www.discourse.org/) is in serious need of a formalized deploy system that is self contained within its codebase but also completely extensible.  Rubber is perfect for this.  So I made a template.

It's basically just a unicorn-nginx-postgres with sidekiq but incorporating their unicorn.rb and nginx.conf files.  Some hiccups still include https://github.com/rubber/rubber/issues/397 (not sure if I can repeat that one) and the fact that some of discourse migrations create postgres extensions but don't have permission.  I worked around that with a task hooked after postgres' bootstrap.  

The main misgiving I had is that Discourse isn't a service like the rest of the templates, it is a codebase with a specific infrastructure.  However, Rubber is well suited to this and the template isn't too tailored to discourse's codebase so it could still be used by others.

I also posted a [gist](https://gist.github.com/ScotterC/6703521) for simple deployment of a discourse app using Rubber.  

I think discourse could have a great relationship with rubber due to it's needs of a deployment system that is both simple to use for newbies and completely configurable.

Here's the discussion on about this on the [Discourse Board](http://meta.discourse.org/t/simple-discourse-deployment-with-rubber/10029)