Migrated from https://oldkea.isc.org/ticket/5658

Current code has many potential problems and was scheduled to use use contexts from the beginning but it was postponed because user contexts in leases were implemented later:

• save/load to a CSV file is implemented but never tested.
• eraseCreateTimestamp() is called only when a STOP event is sent so the timestamp stays in memory without more control

• obviously using an user-context is the right way: extent following the lease one, save in stable storage, etc.

If memory leak on RADIUS accounting experiments are not conclusive this should be tried.