Stick public conversation in a page. Fixes #1601

This is an attempt at improving the onboarding process, specifically by making it easier to understand what exercism is about before making people log in/sign up, as well as setting the tone for the type of conversation that we're encouraging.

The conversation is real—DataWraith and I actually had these back-and-forths on his real code a few weeks ago, and he graciously agreed to share it publicly.

In order to expose this, I want to add a section to the homepage between the three bullet points and the "try it" section.

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**setup**

You don't need the whole site (database, etc) working to work on this page.

1. Fork and clone the repository
2. Set this repository as the upstream `git remote add upstream https://github.com/exercism/exercism.io.git`
3. Fetch the upstream repository `git fetch upstream`
4. Check out the public-conversation branch: `git checkout -b upstream/public-conversation`
5. Start the server with `rackup -p 9000` (or some other port)
6. Open the conversations page at [http://localhost:9000/conversations/1](http://localhost:9000/conversations/1)

The view is in `./lib/app/views/site/conversations.haml`

We could make that Erb if that's easier for you, just let me know (this is a prototype, it's kind of crazy).

The controller action is here (but you probably won't need it) `./lib/app/routes/conversations.rb` and the underlying data is stored here in `./data/conversations`.

Don't even worry about putting the styles in some global stylesheet—all of that is a complete and utter mess. If you stick it in the page for now, that would be totally awesome. We can move it after. Or we can talk about stylesheets :)

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I have no idea what it should look like, but ANYTHING is probably better than what I have right now. I don't know, maybe something like the conversations in iMessage where there's a color difference between the two people and it happens in two columns?

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/cc @breethomas @courtney @bunnymatic @michaelavila

(Side note: I was going to try to make it to the Santa Monica Carbon Five Hacknight last night, but work ended up expanding into the evening hours. Any chance any of you Carbon Fivers go to that?)