* add storagemetadata
* add StorageWiggler;
* fix serverMetadataKey bug
* add metadata tracker in storage tracker
* finish StorageWiggler
* update next storage ID
* change pid to server id
* write metadata when seed SS
* add status json fields
* remove pid based ppw iteration
* fix time expression
* fix tss metadata nonexistence; fix transaction retry when retrieving metadata
* fix checkMetadata bug when store type is wrong
* fix remove storage status json
* format code
* refactor updateNextWigglingStoragePID
* seperate storage metadata tracker and store type tracker
* rename pid
* wiggler stats
* fix completion between waitServerListChange and storageRecruiter
* solve review comments
* rename system key
* fix database lock timeout by adding lock_aware
* format code
* status json
* resolve code format/naming comments
* delete expireNow; change PerpetualStorageWiggleID's value to KeyBackedObjectMap<UID, StorageWiggleValue>
* fix omit start rount
* format code
* status json reset
* solve status json format
* improve status json latency; replace binarywriter/reader to objectwriter/reader; refactor storagewigglerstats transactions
* status timestamp
