* db refactor in progress, refactored kvdb
* kvdb refactor
* removed unused RwLock
* removed unused RwLock
* BlockChainDatabase
* db refactor in progress
* implemented BlockProvider for newdb
* fixed compiling
* newdb TransactionMeta
* newdb tests
* reopen tests for newdb
* replaced old db with new db
* chain_verifier uses new db
* sync module uses refactored db
* check double spends in verification layer
* added Forkable trait to satisfy resolving recursive types by compiler
* new db regtests in progress
* fixed verification and sync unit tests
* fixed miner and rpc unit tests
* implemented fmt::Debug for few structs
* removed commented out code
* fixed bencher target
* removing commented out code, polishing db_refactor pr