refs https://github.com/TryGhost/Team/issues/1001
We fall back to existing behaviour if no API key is present, or if there
is an error communicating with the Twitter API. We're also currently
requesting all the data, which will be thinned down once we understand
what we need.
This also includes a custom renderer for embeds of type "twitter" which
will be used to output the custom HTML for emails
