Fix bugs logging last sign in

[SUPERCILEX]

There are some anonymous accounts with no corresponding entries in the database, leading to them not getting cleaned up properly. Steps to mitigate this issue:

• Write a script to go through all users and nuke those with no entry in the db
• Make the updater function execute every 5 mins and check for ETA to next write using local file. That way we're guaranteed that the write was queued before considering the job done.