Ajv data filtering

[danalexilewis]

Key additions are:

• Using ajv to both validate and filter the data being processed. This guarantees that we wont be leaking private data by accident and consistent data shape for the front end.

• using js-md5 to create a hash of a persons public email to create the users gravatar url.

closes #4 #3

[danalexilewis]

@dazyang I have moved the gravatar computation here so we can show the picture of a person even if they dont want to show their email.

I have also reduced the data shape of general people as per the people.json. I am going to write a similar one for the ambassadors and submit it in another pull request. in the meantime have a review of this.

Note: I have not yet updated the api - as when I do it is going to break the front end as all the keys have been camelCased.