"Fixes" needed for Michaelmas 2022 sync

Needed to run two syncs with different subset of rooms, so added functionality to allow filter of rooms by their building, both only those in the specified building(s) and all excluding those in the specified building(s) with booker.only_buildings and booker.exclude_buildings state keys.

Discovered Booker calendar event (bookings) API endpoint returning 500, possibly due to number of events in response. Hacked the bookings retrieve code to get events one room at a time instead of all at once. Appears to fix. This is seen in scheduled test pipeline failing for Booker staging: https://gitlab.developers.cam.ac.uk/uis/devops/essm/sync-tool/-/jobs/643560

Had to fiddle how tests mock event/bookings responses, avoiding having to recreate a load of additional fixtures.

Fallout from: administration#51