Draft: Servant Api Specification

This PR does 3 things:

1. Specifies a modular definition for the Skete Servant api, along with associated clients and server. The design is granular to facilitate better testing (standalone clients are easier to test when their component apis are separate from the rest of the API)

2. Restructures the project to define a toplevel RestAPI.hs module, with client/server/util definitions in an associated RestAPI/* namespace.

3. Adds the Servant-* dependencies, cleans up old code.

Addresses #21