add a contribute.json file (bug 1074452)

I did my best to find all the data to populate the json file, but l'm assuming I'll need to make a change or two. 
@cvan Can I add the content type when using static.serve? As suggested, I removed the view, and changed the url to the following:
```python
url(r'^(?P<path>contribute\.json)$', 'django.views.static.serve', {'document_root': settings.ROOT})
```
https://github.com/mozilla/airmozilla shows the json on screen, so I'm thinking something's not right...