Kick off migration of Christ's College to using Card API export script

Work with Dave Scott to migrate Christ's college to using the new export script from the Card API rather than the nightly csv exports from the Card Database.

This relies on Christ's being happy to fetch their users from Lookup or locally holding a list of identifiers of users who need access to the college.

Get Christ up and running with the new API and CardClient and raise issues for any follow-up issues that need to be addressed.