gen_details.py: Use user "Date Removed" dates to direct jobs beyond those dates to Unbillable sheet.

[bettingr]

Right now, the script creates a simple list of all users from the Users sheet in BillingConfig to determine whether a job is from an unknown user or not. It should also regard known users from that list who were not active at the time the job ran as "unknown", and direct those jobs to the Unbillable sheet.