First part improvements of PR #2420

First part improvements of PR #2420:
Mainly includes:
 - expiration cleanup improvements
 - map store & expiration/eviction relations
 - adding an upper bound to WBQs
Instead of `MAP_REPLICA_WAIT_SECONDS_FOR_SCHEDULED_TASKS`, this prop can be renamed to `MAP_REPLICA_SCHEDULED_TASK_DELAY_SECONDS`..