can easily set overall quota for all users
- on login, if we can't fallocate initially, but rebalance is on, then allow
login in discard mode, then immediately rebalance, then turn off discard
- - extend user records with optional "bulk" data. Specifically, a user
- avatar/photo or so. This data should be stored along with the user record,
- but probably shouldn't be part of the record itself, since it might be
- large.
- add "homectl unbind" command to remove local user record of an inactive
home dir