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. 
you can just do `return json.load(handle)` and wrap the view with `@json_view` from here: https://github.com/mozilla/zamboni/blob/dfd2dd629d1410587b213d9156aa787be2caff4a/mkt/site/decorators.py#L76