Base listing designs

This adds base CSS and initial designs for listings.

Notes: I added a footer partial because it seems likely that we'll want one but it doesn't have anything in it yet. I also haven't touched the header despite what that first screenshot looks like.

Using Sass + Autoprefixer, no Compass. All of the CSS lives in `app/assets/stylesheets/framework`.

@cherimarie: I'm not able to approve listings running this locally, not sure what's up. I get this error:

```
530-5.5.1 Authentication Required. Learn more at

Extracted source (around line #39):
37    generate_token(:payment_token)
38    save!
39    SubmitterMailer.payment_instructions(self).deliver
40  end
41
42
          
Rails.root: /Users/alexlande/Documents/web/work/2014/jobboard

Application Trace | Framework Trace | Full Trace
app/models/listing.rb:39:in `send_payment_prompt'
app/controllers/listings_controller.rb:46:in `approve'
```

I made a partial to display listings, but I expect that it isn't working on any page except for the search page (which is what I was using for dev). Can't verify that because of the error.

Not sure what your schedule is like. I'll be working on this over the weekend to get stuff up to speed. If you have time to kill, it would be awesome if you want to start incorporating some of these components into other parts of the site. No problem if not though.

I'm going to start moving on to the header + footer next, then head over to Admin sections, most likely.

/cc @cherimarie @eastridge 

Screenshots:

![jobboard](https://f.cloud.github.com/assets/808159/2299468/831beeba-a0cd-11e3-8192-cfddcd6b74a4.png)
![jobboard-post](https://f.cloud.github.com/assets/808159/2299469/8492b9fe-a0cd-11e3-8a1e-1bd1810838a7.png)