Feature discussions focus

OK, here it is - the long awaited discussions pull request!  This PR does a number of things, most notably moving links/news items over to a sidebar, and only showing discussions in the main feed. Other minor items are:

- added a loading animation (CSS class of `.loading-animation` if you want to use it)
- reworded much of the verbage on the site to highlight discussions
- Fixed the RSS URL format for discussions

Here's a screenshot of what the new homepage looks like:

![screen shot 2014-05-19 at 7 56 31 am](https://cloud.githubusercontent.com/assets/657707/3014261/be4a8c64-df55-11e3-9257-a07323180b09.png)

The one gotcha about this PR that I want to get on record is that there is some confusion between the terms "news" and "discussions". Without being able to run database migrations, I needed to leave all URLs in tact and leave all database schemas in tact. I would have preferred to move the homepage to `/discussions` and then all discussion comment pages to `/discussions/abcde`, but the URL is hardcoded in the database ATM.  This is less than ideal, but sort of a requirement of where we're at right now.