A tenancy either covers the whole building or a set of named units; whole-building
tenancies return an empty units array.

status is derived from the tenancy dates rather than stored: Upcoming has not
started, Active is running now, Finished has ended. A tenancy with no end date is
open-ended and stays Active. Use activeOn when you need to ask the same question
about a date other than today.

Rents are returned in full, in the frequency the agent recorded them.