[Breaking change in db!] UI for Buckets stat (#607)

cmd/restapi/apis/db_api.go

cmd/restapi/rest/serve_rest.go

common/size.go

core/blockchain.go

debug-web-ui/package.json

debug-web-ui/src/App.js

debug-web-ui/src/page/DBPage.js

debug-web-ui/src/utils/API.js

debug-web-ui/yarn.lock

eth/api_tracer.go

ethdb/badger_db.go

ethdb/bolt_db.go

ethdb/interface.go

ethdb/kv_abstract.go

ethdb/kv_badger.go

ethdb/kv_bolt.go

ethdb/kv_lmdb.go

ethdb/kv_remote.go

ethdb/memory_database.go

ethdb/mutation.go