* offline block prune
* update
* update
* update and add unit test
* addressed comments from walt
* Addressed comments from walt and Igor
* ensure MPT and snapshot matched
* add one more parameter to indicate blockprune
* update the logic of creating freezerDb
* update flag command description
* expose the function for db inspect the offset/startBlockNumber
* add flags to inspect prune info
* rename flag of reserved-recent-blocks to block-amount-reserved
* addressed comments from walt
* handle the case of command interruption
* refined goimports
* addressed comments from walt
* change the logic as restarting prune after interruption
* addressed comments
* reclaimed freezer logic
* introduce flag to enable/disable check between MPT and snapshot
* update the logic of frozen field in freezerDB
* update the code in all places related to freezer change
* addressed comments from dylan
* update the logic for backup block difficulty
* addressed comments from dylan
