Fapi client integration

Here's a rough working FAPI-client.

Note that these changes are based on those in https://github.com/guardian/facia-scala-client/pull/26, viewing the changes since that branch (instead of master) will reveal the changes that I have made beyond what @janua has done.

The `FAPI` class contains the main interface to the client library. It includes methods that fetch info from Facia and the Content API. Facia's logic is applied to this information before being returned in data types convenient for consumption by other applications.

I'm raising this now so you all see it working, there's still more to do.
e.g. For now we only support standard content trails in the curated content. Some work will need to be done to resolve the various types of snaps into curated content instances.