UX: email configuration and failures of persistent data

[hannesm]

When user or albatross configuration is persisted, and can't be read, mollymawk is complaining loudly. With email configuration, errors are silently discarded.

See

mollymawk/storage.ml

Line 81 in 7dbba0c

| Error _msg -> Ok None)

which should at least emit a warning. Also, having the failure cases uniform would be a much nicer user experience.