Expose homepage data on the API

[gideonthomas]

Fixes #658.

The data returned by /api/homepage looks like:

{
  "leaders": [{
    "name": <string>,
    "role": <string>,
    "location": <string>,
    "image": <string url>,
    "links": {
      "twitter": <string url>,
      "interview": <string url>,
      "linkedIn": <string url>
    },
    "featured": <boolean>, // ignore this for now, will remove later
    "bio": <string>,
    "quote": <string>,
    "affiliations": <array of strings>,
    "internet_health_issues": <array of strings>,
    "partnership_logo": <string url>
  }, ...usually two more],
  
  "news": [{
    "headline": <string>,
    "outlet": <string>,
    "date": "yyyy-mm-dd",
    "link": <string url>,
    "excerpt": <string>,
    "author": <string>,
    "glyph": <string url>,
    "thumbnail": <string url>,
    "is_video": <boolean>, // should be true for the first element
    "featured": <boolean>
  }, ...usually three more],
  
  "highlights": [{
    "id": <integer>,
    "title": <string>,
    "description": <string>,
    "link_url": <string url>,
    "link_label": <string>,
    "image": <string url>,
    "footer": <string>
  }, ...usually two more]
}

@gvn, does the above payload look ok or do you need more data?

[gvn]

As long as these are just curated aggregates of the existing models then it should be good!