Make the CMS work for mobile (responsive UI)

**- Do you want to request a *feature* or report a *bug*?**
Enhancement: It would be nice to quickly check in on a post on the CMS from my phone

**- What is the current behavior?**
The current UI has no consideration for mobile and non-usable from a mobile device.


**- If the current behavior is a bug, please provide the steps to reproduce.**
Look at the https://cms-demo.netlify.com/ from your phone.

**- What is the expected behavior?**
The editor can be ignored for now because it would require a larger scope. However, the editorial workflow and list of posts could be tweaked quickly fit on a mobile screen. Even it was just a list of post.

I recently had a situation where I was AFK and needed to ship a blog post from my phone. My only option was logging into GitHub and merging the PR, but it would have been nice to just hit publish from the CMS

**- Please mention your node.js, and operating system version.**
iPhone 7

Start with the CMS demo at https://cms-demo.netlify.com/ on a phone and inspect the editorial workflow and post list; the issue explicitly excludes the editor. Define the mobile scope around viewing posts and publishing, then verify that those workflows fit and remain usable on a mobile screen.

Written by the indexing model from the issue text.