Allow IbisClient to be used with Lookup behind the API Gateway

Allow the Ibis Client (ideally both Python, PHP and Java - but we could settle just with Python) to be used with the Lookup behind the API Gateway.

We could either support creating an IbisConnection using client credentials from the API Gateway, and / or support using the oauth2 auth code flow to authenticate a user.

This could be used as a good example of a client which can query the API Gateway.

It seems this isn't easily possible at present within python (as I had hoped) by passing in a new requests.session with credentials for the API Gateway, as all request paths start with /api/v1 whereas Lookup behind the API Gateway is rooted at /lookup/v1 (without the api part of the path).