Add an initial implementation

Add a basic implementation of a WebAuth to OAuth2 shim. The common iact, params and fail query flags are respected.

This is very much a first-pass to get 90% of the required functionality working.

We make use of the ucam_wls library to provide the server implementation and glue it together in a single Django view.

As well as unit tests, manual integration testing is possible by visiting http://localhost:8001 in the browser with the development or production environments running. This provides a simple server using mod_ucamwebauth to test authentication.

Closes #1 (closed)