Focus on Chapters page -- modularize the bones of the site

Addresses #27 and #16 

- [x] bring scripts out as includes
- [x] bring css out as includes
- [x] use default as the template
- [x] feed GeoJSON into page to populate chapter listing

To access the chapters as a geojson object:
```
var chapters = {{ site.data.chapters | jsonify }};
```

I also updated `chapters.json` to include all the fields necessary to build the chapters listing.  There were some differences between what was present in `chapters.index`, and `chapters.json`, so I'll need y'all to take a look.  The big win here is you only need to maintain one file and it'll update anywhere you access Chapters from `_data`.

There also seems to be some repetition in data for each chapter; now that I've pulled out the organizers into an array I think we could get rid of `contact`.  `title` and `twitter` are generally the same so we could remove either one.

```
{
  "type": "Feature",
  "properties": {
    "location": "Los Angeles, CA",
    "title": "MaptimeLA",
    "twitter": "MAPTIMELA",
    "contact": "MAPTIMELA",
    "organizers": [
      {"name": "Jonathan Schaeffer", "twitter": "moderndisease"},
      {"name": "Chandler Sterlin", "twitter": "chandlersterlin"},
      {"name": "Jacqui Swartz", "twitter": null},
      {"name": "John Wiseman", "twitter": "lemonodor"},
      {"name": "Machiko Yasuda", "twitter": "machikoyasuda"},
    ],
    "moreInfo": {"type": "Meetup", "url": "http://www.meetup.com/MaptimeLA/"}
  },
  "geometry": {
    "type": "Point",
    "coordinates": [
      -118.24378967285155,
      34.07029354225064
    ]
  }
},
```

Using local versions of mapbox.js/mapbox.css lost a connection to the images for zoom buttons.  They're looking in `/css/images/xxx` for now, we could easily move there or change the css file to look in `/images`.  This still needs to be addressed.

The modularization of JS and CSS basically boils down to using `js` and `css` variables in a page/post's front-matter.  In the default template we have a loop in `head.html` for css files, and just before `</body>` for the scripts as to not block rendering of the DOM.

Questions are welcome!