feat(controller+router+client): application SSL support

Adds Heroku inspired workflow for adding a certificate to an application.  ( Addresses https://github.com/deis/deis/issues/18 )
Please review and see what you think.

Notes:
For the router, I thought that the simplest thing for getting the certs to disk was to use a shell script to write confd templates for each cert pair found in etcd. It's a little bit meta that the confd generator is itself kicked off by confd but it's pretty straightforward.

With regard to the nginx server directives, I have apps with certs listen on both https and http. Would it make sense to have an option to 301 to ssl for cert enabled sites? Perhaps this is an app concern.

From the controller I'm only allowing one cert per app but I kept the Heroku command line convention of removing certs by CN. so `deis certs:remove mydomain.com` instead of `deis certs:remove`. I figured support for multiple certs are inevitable. 


Since this doc is focused for API consumers, let's go with

**New!** `/certs` endpoint for managing application certificates.

How does that sound?